Transgenerational epigenetic inheritance

From Wikipedia, the free encyclopedia

 

Genetically identical mice with different DNA methylation patterns causing kinks in the tail of one but not the other.

 

Transgenerational epigenetic inheritance is the transmission of information from one generation of an organism to the next (i.e., parent–child transmission) that affects the traits of offspring without alteration of the primary structure of DNA (i.e., the sequence of nucleotides)—in other words, epigenetically. The less precise term "epigenetic inheritance" may be used to describe both cell–cell and organism–organism information transfer. Although these two levels of epigenetic inheritance are equivalent in unicellular organisms, they may have distinct mechanisms and evolutionary distinctions in multicellular organisms. 

For some epigenetically influenced traits, the epigenetic marks can be induced by the environment and some marks are heritable, leading some to view epigenetics as a relaxation of the rejection of the inheritance of acquired characteristics (Lamarckism).

Epigenetic categories

Four general categories of epigenetic modification are known:

1. self-sustaining metabolic loops, in which a mRNA or protein product of a gene stimulates transcription of the gene; e.g. Wor1 gene in Candida albicans
2. structural templating in which structures are replicated using a template or scaffold structure on the parent; e.g. the orientation and architecture of cytoskeletal structures, cilia and flagella, prions, proteins that replicate by changing the structure of normal proteins to match their own
3. chromatin marks, in which methyl or acetyl groups bind to DNA nucleotides or histones thereby altering gene expression patterns; e.g. Lcyc gene in Linaria vulgaris described below
4. RNA silencing, in which small RNA strands interfere (RNAi) with the transcription of DNA or translation of mRNA; known only from a few studies, mostly in Caenorhabditis elegans

Inheritance of epigenetic marks

Epigenetic variation may take one of four general forms. Others may yet be elucidated, but currently self-sustaining feedback loops, spatial templating, chromatin marking, and RNA-mediated pathways modify epigenes at the level of individual cells. Epigenetic variation within multicellular organisms may be endogenous, generated by cell–cell signaling (e.g. during cell differentiation early in development), or exogenous, a cellular response to environmental cues.

Removal vs. retention

In sexually reproducing organisms, much of the epigenetic modification within cells is reset during meiosis (e.g. marks at the FLC locus controlling plant vernalization), though some epigenetic responses have been shown to be conserved (e.g. transposon methylation in plants). Differential inheritance of epigenetic marks due to underlying maternal or paternal biases in removal or retention mechanisms may lead to the assignment of epigenetic causation to some parent of origin effects in animals and plants.

Reprogramming

In mammals, epigenetic marks are erased during two phases of the life cycle. Firstly just after fertilization and secondly, in the developing primordial germ cells, the precursors to future gametes. During fertilization the male and female gametes join in different cell cycle states and with different configuration of the genome. The epigenetic marks of the male are rapidly diluted. First, the protamines associated with male DNA are replaced with histones from the female's cytoplasm, most of which are acetylated due to either higher abundance of acetylated histones in the female's cytoplasm or through preferential binding of the male DNA to acetylated histones. Second, male DNA is systematically demethylated in many organisms, possibly through 5-hydroxymethylcytosine. However, some epigenetic marks, particularly maternal DNA methylation, can escape this reprogramming; leading to parental imprinting. 

In the primordial germ cells (PGC) there is a more extensive erasure of epigenetic information. However, some rare sites can also evade erasure of DNA methylation. If epigenetic marks evade erasure during both zygotic and PGC reprogramming events, this could enable transgenerational epigenetic inheritance. 

Recognition of the importance of epigenetic programming to the establishment and fixation of cell line identity during early embryogenesis has recently stimulated interest in artificial removal of epigenetic programming. Epigenetic manipulations may allow for restoration of totipotency in stem cells or cells more generally, thus generalizing regenerative medicine.

Retention

Cellular mechanisms may allow for co-transmission of some epigenetic marks. During replication, DNA polymerases working on the leading and lagging strands are coupled by the DNA processivity factor proliferating cell nuclear antigen (PCNA), which has also been implicated in patterning and strand crosstalk that allows for copy fidelity of epigenetic marks. Work on histone modification copy fidelity has remained in the model phase, but early efforts suggest that modifications of new histones are patterned on those of the old histones and that new and old histones randomly assort between the two daughter DNA strands. With respect to transfer to the next generation, many marks are removed as described above. Emerging studies are finding patterns of epigenetic conservation across generations. For instance, centromeric satellites resist demethylation. The mechanism responsible for this conservation is not known, though some evidence suggests that methylation of histones may contribute. Dysregulation of the promoter methylation timing associated with gene expression dysregulation in the embryo was also identified.

Decay

Whereas the mutation rate in a given 100-base gene may be 10⁻⁷ per generation, epigenes may "mutate" several times per generation or may be fixed for many generations. This raises the question: do changes in epigene frequencies constitute evolution? Rapidly decaying epigenetic effects on phenotypes (i.e. lasting less than three generations) may explain some of the residual variation in phenotypes after genotype and environment are accounted for. However, distinguishing these short-term effects from the effects of the maternal environment on early ontogeny remains a challenge.

Contribution to phenotypes

The relative importance of genetic and epigenetic inheritance is subject to debate. Though hundreds of examples of epigenetic modification of phenotypes have been published, few studies have been conducted outside of the laboratory setting. Therefore, the interactions of genes and epigenes with the environment cannot be inferred despite the central role of environment in natural selection. Experimental methodologies for manipulating epigenetic mechanisms are nascent (e.g.) and will need rigorous demonstration before studies explicitly testing the relative contributions of genotype, environment, and epigenotype are feasible.

In plants

b1 paramutation in maize. The B' allele converts the B-I allele to a B'-like state after interaction in F1 heterozygotes. These converted alleles gain the ability to convert naive B-I alleles in subsequent generations resulting in all progeny displaying lightly pigmented phenotype.

 

Studies concerning transgenerational epigenetic inheritance in plants have been reported as early as the 1950s. One of the earliest and best characterized examples of this is b1 paramutation in maize. The b1 gene encodes a basic helix-loop-helix transcription factor that is involved in the anthocyanin production pathway. When the b1 gene is expressed, the plant accumulates anthocyanin within its tissues, leading to a purple coloration of those tissues. The B-I allele (for B-Intense) has high expression of b1 resulting in the dark pigmentation of the sheath and husk tissues while the B' (pronounced B-prime) allele has low expression of b1 resulting in low pigmentation in those tissues. When homozygous B-I parents are crossed to homozygous B', the resultant F1 offspring all display low pigmentation which is due gene silencing of b1. Unexpectedly, when F1 plants are self-crossed, the resultant F2 generation all display low pigmentation and have low levels of b1 expression. Furthermore, when any F2 plant (including those that are genetically homozygous for B-I) are crossed to homozygous B-I, the offspring will all display low pigmentation and expression of b1. The lack of darkly pigmented individuals in the F2 progeny is an example of non-Mendelian inheritance and further research has suggested that the B-I allele is converted to B' via epigenetic mechanisms. The B' and B-I alleles are considered to be epialleles because they are identical at the DNA sequence level but differ in the level of DNA methylation, siRNA production, and chromosomal interactions within the nucleus. Additionally, plants defective in components of the RNA-directed DNA-methylation pathway show an increased expression of b1 in B' individuals similar to that of B-I, however, once these components are restored, the plant reverts to the low expression state. Although spontaneous conversion from B-I to B' has been observed, a reversion from B' to B-I (green to purple) has never been observed over 50 years and thousands of plants in both greenhouse and field experiments.

Examples of environmentally induced transgenerational epigenetic inheritance in plants has also been reported. In one case, rice plants that were exposed to drought-simulation treatments displayed increased tolerance to drought after 11 generations of exposure and propagation by single-seed descent as compared to non-drought treated plants. Differences in drought tolerance was linked to directional changes in DNA-methylation levels throughout the genome, suggesting that stress-induced heritable changes in DNA-methylation patterns may be important in adaptation to recurring stresses. In another study, plants that were exposed to moderate caterpillar herbivory over multiple generations displayed increased resistance to herbivory in subsequent generations (as measured by caterpillar dry mass) compared to plants lacking herbivore pressure. This increase in herbivore resistance persisted after a generation of growth without any herbivore exposure suggesting that the response was transmitted across generations. The report concluded that components of the RNA-directed DNA-methylation pathway are involved in the increased resistance across generations.

In humans

A number of studies suggest the existence of transgenerational epigenetic inheritance in humans. These include those of the Dutch famine of 1944–45, wherein the offspring born during the famine were smaller than those born the year before the famine and the effects could last for two generations. Moreover, these offspring were found to have an increased risk of glucose intolerance in adulthood. Differential DNA methylation has been found in adult female offspring who had been exposed to famine in utero, but it is unknown whether these differences are present in their germline. It is hypothesized that inhibiting the PIM3 gene may have caused slower metabolism in later generations, but causation has not been proven, only correlation. The phenomenon is sometimes referred to as Dutch Hunger Winter Syndrome. Another study hypothesizes epigenetic changes on the Y chromosome to explain differences in lifespan among the male descendants of prisoners of war in the American Civil War.

The Överkalix study noted sex-specific effects; a greater body mass index (BMI) at 9 years in sons, but not daughters, of fathers who began smoking early. The paternal grandfather's food supply was only linked to the mortality RR of grandsons and not granddaughters. The paternal grandmother's food supply was only associated with the granddaughters' mortality risk ratio. When the grandmother had a good food supply was associated with a twofold higher mortality (RR). This transgenerational inheritance was observed with exposure during the slow growth period (SGP). The SGP is the time before the start of puberty, when environmental factors have a larger impact on the body. The ancestors' SGP in this study was set between the ages of 9-12 for boys and 8–10 years for girls. This occurred in the SGP of both grandparents, or during the gestation period/infant life of the grandmothers, but not during either grandparent's puberty. The father's poor food supply and the mother's good food supply were associated with a lower risk of cardiovascular death.

The loss of genetic expression which results in Prader–Willi syndrome or Angelman syndrome has in some cases been found to be caused by epigenetic changes (or "epimutations") on both the alleles, rather than involving any genetic mutation. In all 19 informative cases, the epimutations that, together with physiological imprinting and therefore silencing of the other allele, were causing these syndromes were localized on a chromosome with a specific parental and grandparental origin. Specifically, the paternally derived chromosome carried an abnormal maternal mark at the SNURF-SNRPN, and this abnormal mark was inherited from the paternal grandmother.

Similarly, epimutations on the MLH1 gene has been found in two individuals with a phenotype of hereditary nonpolyposis colorectal cancer, and without any frank MLH1 mutation which otherwise causes the disease. The same epimutations were also found on the spermatozoa of one of the individuals, indicating the potential to be transmitted to offspring.

A study has shown childhood abuse (defined in this study as "sexual contact, severe physical abuse and/or severe neglect") leads to epigenetic modifications of glucocorticoid receptor expression which play a role in HPA (hypothalamic-pituitary-adrenal) activity. Animal experiments have shown that epigenetic changes depend on mother-infant interactions after birth. In a recent study investigating correlations among maternal stress in pregnancy and methylation in teenagers and their mothers, it has been found that children of women who were abused during pregnancy were significantly more likely than others to have methylated glucocorticoid-receptor genes, which in turn change the response to stress, leading to a higher susceptibility to anxiety.

Effects on fitness

Epigenetic inheritance may only affect fitness if it predictably alters a trait under selection. Evidence has been forwarded that environmental stimuli are important agents in the alteration of epigenes. Ironically, Darwinian evolution may act on these neo-Lamarckian acquired characteristics as well as the cellular mechanisms producing them (e.g. methyltransferase genes). Epigenetic inheritance may confer a fitness benefit to organisms that deal with environmental changes at intermediate timescales. Short-cycling changes are likely to have DNA-encoded regulatory processes, as the probability of the offspring needing to respond to changes multiple times during their lifespans is high. On the other end, natural selection will act on populations experiencing changes on longer-cycling environmental changes. In these cases, if epigenetic priming of the next generation is deleterious to fitness over most of the interval (e.g. misinformation about the environment), these genotypes and epigenotypes will be lost. For intermediate time cycles, the probability of the offspring encountering a similar environment is sufficiently high without substantial selective pressure on individuals lacking a genetic architecture capable of responding to the environment. Naturally, the absolute lengths of short, intermediate, and long environmental cycles will depend on the trait, the length of epigenetic memory, and the generation time of the organism. Much of the interpretation of epigenetic fitness effects centers on the hypothesis that epigenes are important contributors to phenotypes, which remains to be resolved.

Deleterious effects

Inherited epigenetic marks may be important for regulating important components of fitness. In plants, for instance, the Lcyc gene in Linaria vulgaris controls the symmetry of the flower. Linnaeus first described radially symmetric mutants, which arise when Lcyc is heavily methylated. Given the importance of floral shape to pollinators, methylation of Lcyc homologues (e.g. CYCLOIDEA) may have deleterious effects on plant fitness. In animals, numerous studies have shown that inherited epigenetic marks can increase susceptibility to disease. Transgenerational epigenetic influences are also suggested to contribute to disease, especially cancer, in humans. Tumor methylation patterns in gene promotors have been shown to correlate positively with familial history of cancer. Furthermore, methylation of the MSH2 gene is correlated with early-onset colorectal and endometrial cancers.

Putatively adaptive effects

Experimentally demethylated seeds of the model organism Arabidopsis thaliana have significantly higher mortality, stunted growth, delayed flowering, and lower fruit set, indicating that epigenes may increase fitness. Furthermore, environmentally induced epigenetic responses to stress have been shown to be inherited and positively correlated with fitness. In animals, communal nesting changes mouse behavior increasing parental care regimes and social abilities that are hypothesized to increase offspring survival and access to resources (such as food and mates), respectively.

Macroevolutionary patterns

Inherited epigenetic effects on phenotypes have been documented in bacteria, protists, fungi, plants, and animals. Though no systematic study of epigenetic inheritance has been conducted (most focus on model organisms), there is preliminary evidence that this mode of inheritance is more important in plants than in animals. The early differentiation of animal germlines is likely to preclude epigenetic marking occurring later in development, while in plants and fungi somatic cells may be incorporated into the germ line.

Life history patterns may also contribute to the occurrence of epigenetic inheritance. Sessile organisms, those with low dispersal capability, and those with simple behavior may benefit most from conveying information to their offspring via epigenetic pathways. Geographic patterns may also emerge, where highly variable and highly conserved environments might host fewer species with important epigenetic inheritance.

Controversies

Humans have long recognized that traits of the parents are often seen in offspring. This insight led to the practical application of selective breeding of plants and animals, but did not address the central question of inheritance: how are these traits conserved between generations, and what causes variation? Several positions have been held in the history of evolutionary thought.

Blending vs. particulate inheritance

Blending inheritance leads to the averaging out of every characteristic, which as the engineer Fleeming Jenkin pointed out, makes evolution by natural selection impossible.

 

Addressing these related questions, scientists during the time of the Enlightenment largely argued for the blending hypothesis, in which parental traits were homogenized in the offspring much like buckets of different colored paint being mixed together. Critics of Charles Darwin's On the Origin of Species, pointed out that under this scheme of inheritance, variation would quickly be swamped by the majority phenotype. In the paint bucket analogy, this would be seen by mixing two colors together and then mixing the resulting color with only one of the parent colors 20 times; the rare variant color would quickly fade.

Unknown to most of the European scientific community, a monk by the name of Gregor Mendel had resolved the question of how traits are conserved between generations through breeding experiments with pea plants. Charles Darwin thus did not know of Mendel's proposed "particulate inheritance" in which traits were not blended but passed to offspring in discrete units that we now call genes. Darwin came to reject the blending hypothesis even though his ideas and Mendel's were not unified until the 1930s, a period referred to as the modern synthesis.

Inheritance of innate vs. acquired characteristics

In his 1809 book, Philosophie Zoologique, Jean-Baptiste Lamarck recognized that each species experiences a unique set of challenges due to its form and environment. Thus, he proposed that the characters used most often would accumulate a "nervous fluid." Such acquired accumulations would then be transmitted to the individual's offspring. In modern terms, a nervous fluid transmitted to offspring would be a form of epigenetic inheritance.

Lamarckism, as this body of thought became known, was the standard explanation for change in species over time when Charles Darwin and Alfred Russel Wallace co-proposed a theory of evolution by natural selection in 1859. Responding to Darwin and Wallace's theory, a revised neo-Lamarckism attracted a small following of biologists, though the Lamarckian zeal was quenched in large part due to Weismann's famous experiment in which he cut off the tails of mice over several successive generations without having any effect on tail length. Thus the emergent consensus that acquired characteristics could not be inherited became canon.

Revision of evolutionary theory

Non-genetic variation and inheritance, however, proved to be quite common. Concurrent to the modern evolutionary synthesis (unifying Mendelian genetics and natural selection), C. H. Waddington was working to unify developmental biology and genetics. In so doing, he coined the word "epigenetic" to represent the ordered differentiation of embryonic cells into functionally distinct cell types despite having identical primary structure of their DNA. Waddington's epigenetics was sporadically discussed, becoming more of a catch-all for puzzling non-genetic heritable characters rather than advancing the body of inquiry. Consequently, the definition of Waddington's word has itself evolved, broadening beyond the subset of developmentally signaled, inherited cell specialization. 

Some scientists have questioned if epigenetic inheritance compromises the foundation of the modern synthesis. Outlining the central dogma of molecular biology, Francis Crick succinctly stated, "DNA is held in a configuration by histone[s] so that it can act as a passive template for the simultaneous synthesis of RNA and protein[s]. None of the detailed 'information' is in the histone." However, he closes the article stating, "this scheme explains the majority of the present experimental results!" Indeed, the emergence of epigenetic inheritance (in addition to advances in the study of evolutionary-development, phenotypic plasticity, evolvability, and systems biology) has strained the current framework of the modern evolutionary synthesis, and prompted the re-examination of previously dismissed evolutionary mechanisms.

There has been much critical discussion of mainstream evolutionary theory by Edward J Steele, Robyn A Lindley and colleagues, Fred Hoyle and N. Chandra Wickramasinghe, Yongsheng Liu Denis Noble, John Mattick and others that the logical inconsistencies as well as Lamarckian Inheritance effects involving direct DNA modifications, as well as the just described indirect, viz. epigenetic, transmissions, challenge conventional thinking in evolutionary biology and adjacent fields.

Mendelian inheritance

From Wikipedia, the free encyclopedia

Gregor Mendel, the Moravian Augustinian monk who founded the modern science of genetics

Mendelian inheritance is a type of biological inheritance that follows the laws originally proposed by Gregor Mendel in 1865 and 1866 and re-discovered in 1900. These laws were initially controversial. When Mendel's theories were integrated with the Boveri–Sutton chromosome theory of inheritance by Thomas Hunt Morgan in 1915, they became the core of classical genetics. Ronald Fisher combined these ideas with the theory of natural selection in his 1930 book The Genetical Theory of Natural Selection, putting evolution onto a mathematical footing and forming the basis for population genetics within the modern evolutionary synthesis.

History

The principles of Mendelian inheritance were named for and first derived by Gregor Johann Mendel, a nineteenth-century Moravian monk who formulated his ideas after conducting simple hybridisation experiments with pea plants (Pisum sativum) he had planted in the garden of his monastery. Between 1856 and 1863, Mendel cultivated and tested some 5,000 pea plants. From these experiments, he induced two generalizations which later became known as Mendel's Principles of Heredity or Mendelian inheritance. He described these principles in a two-part paper, Versuche über Pflanzen-Hybriden (Experiments on Plant Hybridization), that he read to the Natural History Society of Brno on 8 February and 8 March 1865, and which was published in 1866.

Mendel's conclusions were largely ignored by the vast majority. Although they were not completely unknown to biologists of the time, they were not seen as generally applicable, even by Mendel himself, who thought they only applied to certain categories of species or traits. A major block to understanding their significance was the importance attached by 19th-century biologists to the apparent blending of many inherited traits in the overall appearance of the progeny, now known to be due to multi-gene interactions, in contrast to the organ-specific binary characters studied by Mendel. In 1900, however, his work was "re-discovered" by three European scientists, Hugo de Vries, Carl Correns, and Erich von Tschermak. The exact nature of the "re-discovery" has been debated: De Vries published first on the subject, mentioning Mendel in a footnote, while Correns pointed out Mendel's priority after having read De Vries' paper and realizing that he himself did not have priority. De Vries may not have acknowledged truthfully how much of his knowledge of the laws came from his own work and how much came only after reading Mendel's paper. Later scholars have accused Von Tschermak of not truly understanding the results at all.

Regardless, the "re-discovery" made Mendelism an important but controversial theory. Its most vigorous promoter in Europe was William Bateson, who coined the terms "genetics" and "allele" to describe many of its tenets. The model of heredity was contested by other biologists because it implied that heredity was discontinuous, in opposition to the apparently continuous variation observable for many traits. Many biologists also dismissed the theory because they were not sure it would apply to all species. However, later work by biologists and statisticians such as Ronald Fisher showed that if multiple Mendelian factors were involved in the expression of an individual trait, they could produce the diverse results observed, and thus showed that Mendelian genetics is compatible with natural selection. Thomas Hunt Morgan and his assistants later integrated Mendel's theoretical model with the chromosome theory of inheritance, in which the chromosomes of cells were thought to hold the actual hereditary material, and created what is now known as classical genetics, a highly successful foundation which eventually cemented Mendel's place in history. 

Mendel's findings allowed scientists such as Fisher and J.B.S. Haldane to predict the expression of traits on the basis of mathematical probabilities. An important aspect of Mendel's success can be traced to his decision to start his crosses only with plants he demonstrated were true-breeding. He only measured discrete (binary) characteristics, such as color, shape, and position of the seeds, rather than quantitatively variable characteristics. He expressed his results numerically and subjected them to statistical analysis. His method of data analysis and his large sample size gave credibility to his data. He had the foresight to follow several successive generations (F2, F3) of pea plants and record their variations. Finally, he performed "test crosses" (backcrossing descendants of the initial hybridization to the initial true-breeding lines) to reveal the presence and proportions of recessive characters.

Mendel's laws

A Punnett square for one of Mendel's pea plant experiments – self-fertilization of the F1 generation

 

Mendel discovered that, when he crossed purebred white flower and purple flower pea plants (the parental or P generation), the result was not a blend. Rather than being a mix of the two, the offspring (known as the F₁ generation) was purple-flowered. When Mendel self-fertilized the F₁ generation pea plants, he obtained a purple flower to white flower ratio in the F₂ generation of 3 to 1. The results of this cross are tabulated in the Punnett square to the right.

He then conceived the idea of heredity units, which he called "factors". Mendel found that there are alternative forms of factors—now called genes—that account for variations in inherited characteristics. For example, the gene for flower color in pea plants exists in two forms, one for purple and the other for white. The alternative "forms" are now called alleles. For each biological trait, an organism inherits two alleles, one from each parent. These alleles may be the same or different. An organism that has two identical alleles for a gene is said to be homozygous for that gene (and is called a homozygote). An organism that has two different alleles for a gene is said be heterozygous for that gene (and is called a heterozygote).

Mendel hypothesized that allele pairs separate randomly, or segregate, from each other during the production of gametes: egg and sperm. Because allele pairs separate during gamete production, a sperm or egg carries only one allele for each inherited trait. When sperm and egg unite at fertilization, each contributes its allele, restoring the paired condition in the offspring. This is called the Law of Segregation. Mendel also found that each pair of alleles segregates independently of the other pairs of alleles during gamete formation. This is known as the Law of Independent Assortment.

The genotype of an individual is made up of the many alleles it possesses. An individual's physical appearance, or phenotype, is determined by its alleles as well as by its environment. The presence of an allele does not mean that the trait will be expressed in the individual that possesses it. If the two alleles of an inherited pair differ (the heterozygous condition), then one determines the organism’s appearance and is called the dominant allele; the other has no noticeable effect on the organism’s appearance and is called the recessive allele. Thus, in the example above the dominant purple flower allele will hide the phenotypic effects of the recessive white flower allele. This is known as the Law of Dominance but it is not a transmission law: it concerns the expression of the genotype. The upper case letters are used to represent dominant alleles whereas the lowercase letters are used to represent recessive alleles.

Mendel's laws of inheritance

Law	Definition
Law of segregation	During gamete formation, the alleles for each gene segregate from each other so that each gamete carries only one allele for each gene.
Law of independent assortment	Genes of different traits can segregate independently during the formation of gametes.
Law of dominance	Some alleles are dominant while others are recessive; an organism with at least one dominant allele will display the effect of the dominant allele.

In the pea plant example above, the capital "B" represents the dominant allele for purple flowers and lowercase "b" represents the recessive allele for white flowers. Both parental plants were true-breeding, and one parental variety had two alleles for purple flowers (BB) while the other had two alleles for white flowers (bb). As a result of fertilization, the F₁ hybrids each inherited one allele for purple flowers and one for white. All the F₁ hybrids (Bb) had purple flowers, because the dominant B allele has its full effect in the heterozygote, while the recessive b allele has no effect on flower color. For the F₂ plants, the ratio of plants with purple flowers to those with white flowers (3:1) is called the phenotypic ratio. The genotypic ratio, as seen in the Punnett square, is 1 BB : 2 Bb : 1 bb.

Law of Segregation of genes (the "First Law")

Figure 1 Dominant and recessive phenotypes.
(1) Parental generation.
(2) F₁ generation.
(3) F₂ generation. Dominant (red) and recessive (white) phenotype look alike in the F₁ (first) generation and show a 3:1 ratio in the F₂ (second) generation.

 

The Law of Segregation states that every individual organism contains two alleles for each trait, and that these alleles segregate (separate) during meiosis such that each gamete contains only one of the alleles. An offspring thus receives a pair of alleles for a trait by inheriting homologous chromosomes from the parent organisms: one allele for each trait from each parent.

Molecular proof of this principle was subsequently found through observation of meiosis by two scientists independently, the German botanist Oscar Hertwig in 1876, and the Belgian zoologist Edouard Van Beneden in 1883. Paternal and maternal chromosomes get separated in meiosis and the alleles with the traits of a character are segregated into two different gametes. Each parent contributes a single gamete, and thus a single, randomly successful allele copy to their offspring and fertilization.

Law of Independent Assortment (the "Second Law")

According to independent assortment, 3 homologous pairs create 8 possible combinations, all equally likely to be fertilized. The equation to determine the number of possible combinations given the number of homologous pairs = 2^x (x = number of homologous pairs)

 

Figure 2 Dihybrid cross. The phenotypes of two independent traits show a 9:3:3:1 ratio in the F₂ generation. In this example, coat color is indicated by B (brown, dominant) or b (white), while tail length is indicated by S (short, dominant) or s (long). When parents are homozygous for each trait (SSbb and ssBB), their children in the F₁ generation are heterozygous at both loci and only show the dominant phenotypes (SsbB). If the children mate with each other, in the F₂ generation all combinations of coat color and tail length occur: 9 are brown/short (purple boxes), 3 are white/short (pink boxes), 3 are brown/long (blue boxes) and 1 is white/long (green box).

 

The Law of Independent Assortment states that alleles for separate traits are passed independently of one another. That is, the biological selection of an allele for one trait has nothing to do with the selection of an allele for any other trait. Mendel found support for this law in his dihybrid cross experiments (Fig. 1). In his monohybrid crosses, an idealized 3:1 ratio between dominant and recessive phenotypes resulted. In dihybrid crosses, however, he found a 9:3:3:1 ratios (Fig. 2). This shows that each of the two alleles is inherited independently from the other, with a 3:1 phenotypic ratio for each. 

Independent assortment occurs in eukaryotic organisms during meiotic metaphase I, and produces a gamete with a mixture of the organism's chromosomes. The physical basis of the independent assortment of chromosomes is the random orientation of each bivalent chromosome along the metaphase plate with respect to the other bivalent chromosomes. Along with crossing over, independent assortment increases genetic diversity by producing novel genetic combinations.

There are many violations of independent assortment due to genetic linkage.

Of the 46 chromosomes in a normal diploid human cell, half are maternally derived (from the mother's egg) and half are paternally derived (from the father's sperm). This occurs as sexual reproduction involves the fusion of two haploid gametes (the egg and sperm) to produce a new organism having the full complement of chromosomes. During gametogenesis—the production of new gametes by an adult—the normal complement of 46 chromosomes needs to be halved to 23 to ensure that the resulting haploid gamete can join with another gamete to produce a diploid organism. An error in the number of chromosomes, such as those caused by a diploid gamete joining with a haploid gamete, is termed aneuploidy. 

In independent assortment, the chromosomes that result are randomly sorted from all possible maternal and paternal chromosomes. Because zygotes end up with a random mix instead of a pre-defined "set" from either parent, chromosomes are therefore considered assorted independently. As such, the zygote can end up with any combination of paternal or maternal chromosomes. Any of the possible variants of a zygote formed from maternal and paternal chromosomes will occur with equal frequency. For human gametes, with 23 pairs of chromosomes, the number of possibilities is 2²³ or 8,388,608 possible combinations. The zygote will normally end up with 23 chromosomes pairs, but the origin of any particular chromosome will be randomly selected from paternal or maternal chromosomes. This contributes to the genetic variability of progeny.

Law of Dominance (the "Third Law")

Mendel's Law of Dominance states that recessive alleles will always be masked by dominant alleles. Therefore, a cross between a homozygous dominant and a homozygous recessive will always express the dominant phenotype, while still having a heterozygous genotype. The Law of Dominance can be explained easily with the help of a mono hybrid cross experiment:- In a cross between two organisms pure for any pair (or pairs) of contrasting traits (characters), the character that appears in the F1 generation is called "dominant" and the one which is suppressed (not expressed) is called "recessive." Each character is controlled by a pair of dissimilar factors. Only one of the characters expresses. The one which expresses in the F1 generation is called Dominant. However, the law of dominance is not universally applicable.

Mendelian trait

A Mendelian trait is one that is controlled by a single locus in an inheritance pattern. In such cases, a mutation in a single gene can cause a disease that is inherited according to Mendel's laws. Examples include sickle-cell anemia, Tay–Sachs disease, cystic fibrosis and xeroderma pigmentosa. A disease controlled by a single gene contrasts with a multi-factorial disease, like heart disease, which is affected by several loci (and the environment) as well as those diseases inherited in a non-Mendelian fashion.

Non-Mendelian inheritance

In four o'clock plants, the alleles for red and white flowers show incomplete dominance. As seen in the F₁ generation, heterozygous (wr) plants have "pink" flowers—a mix of "red" (rr) and "white" (ww) coloring. The F₂ generation shows a 1:2:1 ratio of red:pink:white

Mendel explained inheritance in terms of discrete factors—genes—that are passed along from generation to generation according to the rules of probability. Mendel's laws are valid for all sexually reproducing organisms, including garden peas and human beings. However, Mendel's laws stop short of explaining some patterns of genetic inheritance. For most sexually reproducing organisms, cases where Mendel's laws can strictly account for the patterns of inheritance are relatively rare. Often, the inheritance patterns are more complex. 

The F₁ offspring of Mendel's pea crosses always looked like one of the two parental varieties. In this situation of "complete dominance," the dominant allele had the same phenotypic effect whether present in one or two copies. But for some characteristics, the F₁ hybrids have an appearance in between the phenotypes of the two parental varieties. A cross between two four o'clock (Mirabilis jalapa) plants shows this common exception to Mendel's principles. Some alleles are neither dominant nor recessive. The F₁ generation produced by a cross between red-flowered (RR) and white flowered (WW) Mirabilis jalapa plants consists of pink-colored flowers. Neither allele is dominant in this case. This third phenotype results from flowers of the heterzygote having less red pigment than the red homozygotes. Cases in which one allele is not completely dominant over another are called incomplete dominance. In incomplete dominance, the heterozygous phenotype lies somewhere between the two homozygous phenotypes.

A similar situation arises from codominance, in which the phenotypes produced by both alleles are clearly expressed. For example, in certain varieties of chicken, the allele for black feathers is codominant with the allele for white feathers. Heterozygous chickens have a color described as "erminette", speckled with black and white feathers. Unlike the blending of red and white colors in heterozygous four o'clocks, black and white colors appear separately in chickens. Many human genes, including one for a protein that controls cholesterol levels in the blood, show codominance, too. People with the heterozygous form of this gene produce two different forms of the protein, each with a different effect on cholesterol levels.

In Mendelian inheritance, genes have only two alleles, such as a and A. In nature, such genes exist in several different forms and are therefore said to have multiple alleles. A gene with more than two alleles is said to have multiple alleles. An individual, of course, usually has only two copies of each gene, but many different alleles are often found within a population. One of the best-known examples is coat color in rabbits. A rabbit's coat color is determined by a single gene that has at least four different alleles. The four known alleles display a pattern of simple dominance that can produce four coat colors. Many other genes have multiple alleles, including the human genes for ABO blood type.

Furthermore, many traits are produced by the interaction of several genes. Traits controlled by two or more genes are said to be polygenic traits. Polygenic means "many genes." For example, at least three genes are involved in making the reddish-brown pigment in the eyes of fruit flies. Polygenic traits often show a wide range of phenotypes. The broad variety of skin color in humans comes about partly because at least four different genes probably control this trait.

White supremacy

From Wikipedia, the free encyclopedia

White supremacy or white supremacism is the racist belief that white people are superior to people of other races and therefore should be dominant over them. White supremacy has roots in scientific racism, and it often relies on pseudoscientific arguments. Like most similar movements such as neo-Nazism, white supremacists typically oppose members of other races as well as Jews.

The term is also typically used to describe a political ideology that perpetuates and maintains the social, political, historical, or institutional domination by white people (as evidenced by historical and contemporary sociopolitical structures such as the Atlantic slave trade, Jim Crow laws in the United States, and apartheid in South Africa). Different forms of white supremacism put forth different conceptions of who is considered white, and different groups of white supremacists identify various racial and cultural groups as their primary enemy.

In academic usage, particularly in usage which draws on critical race theory or intersectionality, the term "white supremacy" can also refer to a political or socioeconomic system, in which white people enjoy a structural advantage (privilege) over other ethnic groups, on both a collective and individual level.

History

White supremacy has ideological foundations that date back to 17th-century scientific racism, the predominant paradigm of human variation that helped shape international relations and racial policy from the latter part of the Age of Enlightenment until the late 20th century (marked by decolonization and the abolition of apartheid in South Africa in 1991, followed by that country's first multiracial elections in 1994).

The Battle of Liberty Place monument in Louisiana was erected in 1891 by the white-dominated New Orleans government. An inscription added in 1932 states that the 1876 US Presidential Election "recognized white supremacy in the South and gave us our state". It was removed in 2017 and placed in storage.

 

Ku Klux Klan parade in Washington, D.C. in 1926

United States

White supremacy was dominant in the United States both before and after the American Civil War, and it also persisted for decades after the Reconstruction Era. In the antebellum South, this included the holding of African Americans in chattel slavery, in which four million of them were denied freedom. The outbreak of the Civil War saw the desire to uphold white supremacy being cited as a cause for state secession and the formation of the Confederate States of America. In an editorial about Native Americans in 1890, author L. Frank Baum wrote: "The Whites, by law of conquest, by justice of civilization, are masters of the American continent, and the best safety of the frontier settlements will be secured by the total annihilation of the few remaining Indians."

In some parts of the United States, many people who were considered non-white were disenfranchised, barred from government office, and prevented from holding most government jobs well into the second half of the 20th century. Professor Leland T. Saito of the University of Southern California writes: "Throughout the history of the United States, race has been used by whites for legitimizing and creating difference and social, economic and political exclusion." The Naturalization Act of 1790 limited U.S. citizenship to whites only.

The denial of social and political freedom to minorities continued into the mid-20th century, resulting in the civil rights movement. Sociologist Stephen Klineberg has stated that U.S. immigration laws prior to 1965 clearly declared "that Northern Europeans are a superior subspecies of the white race". The Immigration and Nationality Act of 1965 opened entry to the U.S. to immigrants other than traditional Northern European and Germanic groups, and significantly altered the demographic mix in the U.S as a result. Many U.S. states banned interracial marriage through anti-miscegenation laws until 1967, when these laws were invalidated by the Supreme Court of the United States' decision in Loving v. Virginia. These mid-century gains had a major impact on white Americans' political views; segregation and white racial superiority, which had been publicly endorsed in the 1940s, became minority views within the white community by the mid-1970s, and continued to decline into 1990s polls to a single-digit percentage. For sociologist Howard Winant, these shifts marked the end of "monolithic white supremacy" in the United States.

After the mid-1960s, white supremacy remained an important ideology to the American far-right. According to Kathleen Belew, a historian of race and racism in the United States, white militancy shifted after the Vietnam War from supporting the existing racial order to a more radical position—self-described as "white power" or "white nationalism"—committed to overthrowing the United States government and establishing a white homeland. Such anti-government militia organizations are one of three major strands of violent right-wing movements in the United States, with white supremacist groups (such as the Ku Klux Klan, neo-Nazi organizations, and racist skinheads) and a religious fundamentalist movement (such as Christian Identity) being the other two. Howard Winant writes that, "On the far right the cornerstone of white identity is belief in an ineluctable, unalterable racialized difference between whites and nonwhites." In the view of philosopher Jason Stanley, white supremacy in the United States is an example of the fascist politics of hierarchy, in that it "demands and implies a perpetual hierarchy" in which whites dominate and control non-whites.

Some academics argue that outcomes from the 2016 United States Presidential Election reflect ongoing challenges with white supremacy. Psychologist Janet Helms suggested that the normalizing behaviors of social institutions of education, government, and healthcare are organized around the "birthright of...the power to control society's resources and determine the rules for [those resources]". Educators, literary theorists, and other political experts have raised similar questions, connecting the scapegoating of disenfranchised populations to white superiority.

On July 23, 2019, Christopher A. Wray, the head of the FBI, said at a Senate Judiciary Committee hearing that the agency had made around 100 domestic terrorism arrests since October 1, 2018, and that the majority of them were connected in some way with white supremacy. Wray said that the Bureau was "aggressively pursuing [domestic terrorism] using both counterterrorism resources and criminal investigative resources and partnering closely with our state and local partners," but said that it was focused on the violence itself and not on its ideological basis. A similar number of arrests had been made for instances of international terrorism. In the past, Wray has said that white supremacy was a significant and "pervasive" threat to the U.S.

Effect of the media

White supremacism has been depicted in music videos, feature films, documentaries, journal entries, and on social media. The 1915 silent drama film The Birth of a Nation followed the rising racial, economic, political, and geographic tensions leading up to the Emancipation Proclamation and the Southern Reconstruction era that was the genesis of the Ku Klux Klan. Nearly 100 years later, A 2016 film of the same name, was released to tell the story of Nat Turner's Slave Rebellion. It told the story of a literate slave, Nat Turner, and his pursuits to battle injustice between slave owners and slaves. Director Nate Parker stated he has "reclaimed this title and re-purposed it as a tool to challenge racism and white supremacy in America, to inspire a riotous disposition toward any and all injustice in this country (and abroad) and to promote the kind of honest confrontation that will galvanize our society toward healing and sustained systemic change."

David Duke, a former Grand Wizard of the Ku Klux Klan, believed that the Internet was going to create a "chain reaction of racial enlightenment that will shake the world." Jessie Daniels also said that racist groups see the Internet as a way to spread their ideologies, influence others and gain supporters. Legal scholar Richard Hasen describes a "dark side" of social media:

There certainly were hate groups before the Internet and social media. [But with social media] it just becomes easier to organize, to spread the word, for people to know where to go. It could be to raise money, or it could be to engage in attacks on social media. Some of the activity is virtual. Some of it is in a physical place. Social media has lowered the collective-action problems that individuals who might want to be in a hate group would face. You can see that there are people out there like you. That's the dark side of social media.

With the emergence of Twitter in 2006, and platforms such as Stormfront which was launched in 1996, an alt-right portal for white supremacists with similar beliefs, both adults and children, was provided in which they were given a way to connect. Daniels discussed the emergence of other social media outlets such as 4chan and Reddit, which meant that the "spread of white nationalist symbols and ideas could be accelerated and amplified". Sociologist Kathleen Blee notes that the anonymity which the Internet provides can make it difficult to track the extent of white supremacist activity in the country, but nevertheless she and other experts see an increase in the amount of hate crimes and white supremacist violence. In the latest wave of white supremacy, in the age of the Internet, Blee sees the movement as having primarily become a virtual one, in which divisions between groups become blurred: "[A]ll these various groups that get jumbled together as the alt-right and people who have come in from the more traditional neo-Nazi world. We're in a very different world now."

A series on YouTube hosted by the grandson of Thomas Robb, the national director of the Knights of the Ku Klux Klan, "presents the Klan's ideology in a format aimed at kids — more specifically, white kids." The short episodes inveigh against race-mixing, and extol other white supremacist ideologies. A short documentary published by TRT describes the experience of Imran Garda, a journalist of Indian descent, who met with Thomas Robb and a traditional KKK group. A sign that greets people who enter the town states "Diversity is a code for white genocide." The KKK group interviewed in the documentary summarizes its ideals, principles, and beliefs, which are emblematic of white supremacists in the United States. The comic book super hero Captain America, in an ironic co-optation, has been used for dog whistle politics by the alt-right in college campus recruitment in 2017.

British Commonwealth

In 1937, Winston Churchill told the Palestine Royal Commission: "I do not admit for instance, that a great wrong has been done to the Red Indians of America or the black people of Australia. I do not admit that a wrong has been done to these people by the fact that a stronger race, a higher-grade race, a more worldly wise race to put it that way, has come in and taken their place." British historian Richard Toye, author of Churchill's Empire, said that "Churchill did think that white people were superior."

South Africa

A number of Southern African nations experienced severe racial tension and conflict during global decolonization, particularly as white Africans of European ancestry fought to protect their preferential social and political status. Racial segregation in South Africa began in colonial times under the Dutch Empire, and it continued when the British took over the Cape of Good Hope in 1795. Apartheid was introduced as an officially structured policy by the Afrikaner-dominated National Party after the general election of 1948. Apartheid's legislation divided inhabitants into four racial groups—"black", "white", "coloured", and "Indian", with coloured divided into several sub-classifications. In 1970, the Afrikaner-run government abolished non-white political representation, and starting that year black people were deprived of South African citizenship. South Africa abolished apartheid in 1991.

Rhodesia

In Rhodesia a predominantly white government issued its own unilateral declaration of independence from the United Kingdom during an unsuccessful attempt to avoid immediate majority rule.^[40] Following the Rhodesian Bush War which was fought by African nationalists, Rhodesian prime minister Ian Smith acceded to biracial political representation in 1978 and the state achieved recognition from the United Kingdom as Zimbabwe in 1980.

Poster of the Nazi paper Der Stürmer (1935) condemning relations between Jews and non-Jewish Germans

Germany

Nazism promoted the idea of a superior Germanic people or Aryan race in Germany during the early 20th century. Notions of white supremacy and Aryan racial superiority were combined in the 19th century, with white supremacists maintaining the belief that white people were members of an Aryan "master race" which was superior to other races, particularly the Jews, who were described as the "Semitic race", Slavs, and Gypsies, which they associated with "cultural sterility". Arthur de Gobineau, a French racial theorist and aristocrat, blamed the fall of the ancien régime in France on racial degeneracy caused by racial intermixing, which he argued had destroyed the "purity" of the Nordic or Germanic race. Gobineau's theories, which attracted a strong following in Germany, emphasized the existence of an irreconcilable polarity between Aryan or Germanic peoples and Jewish culture.

As the Nazi Party's chief racial theorist, Alfred Rosenberg oversaw the construction of a human racial "ladder" that justified Hitler's racial and ethnic policies. Rosenberg promoted the Nordic theory, which regarded Nordics as the "master race", superior to all others, including other Aryans (Indo-Europeans). Rosenberg got the racial term Untermensch from the title of Klansman Lothrop Stoddard's 1922 book The Revolt Against Civilization: The Menace of the Under-man. It was later adopted by the Nazis from that book's German version Der Kulturumsturz: Die Drohung des Untermenschen (1925). Rosenberg was the leading Nazi who attributed the concept of the East-European "under man" to Stoddard. An advocate of the U.S. immigration laws that favored Northern Europeans, Stoddard wrote primarily on the alleged dangers posed by "colored" peoples to white civilization, and wrote The Rising Tide of Color Against White World-Supremacy in 1920. In establishing a restrictive entry system for Germany in 1925, Hitler wrote of his admiration for America's immigration laws: "The American Union categorically refuses the immigration of physically unhealthy elements, and simply excludes the immigration of certain races."

German praise for America's institutional racism, previously found in Hitler's Mein Kampf, was continuous throughout the early 1930's, and Nazi lawyers were advocates of the use of American models. Race-based U.S. citizenship and anti-miscegenation laws directly inspired the Nazis' two principal Nuremberg racial laws—the Citizenship Law and the Blood Law. In order to preserve the Aryan or Nordic race, the Nazis introduced the Nuremberg Laws in 1935, which forbade sexual relations and marriages between Germans and Jews, and later between Germans and Romani and Slavs. The Nazis used the Mendelian inheritance theory to argue that social traits were innate, claiming that there was a racial nature associated with certain general traits such as inventiveness or criminal behavior.

According to the 2012 annual report of Germany's interior intelligence service, the Federal Office for the Protection of the Constitution, at the time there were 26,000 right-wing extremists living in Germany, including 6000 neo-Nazis.

Russia

Neo-Nazi organisations embracing white supremacist ideology are present in many countries of the world. In 2007, it was claimed that Russian neo-Nazis accounted for "half of the world's total".

Ukraine

In June 2015, Democratic Representative John Conyers and his Republican colleague Ted Yoho offered bipartisan amendments to block the U.S. military training of Ukraine's Azov Battalion — called a "neo-Nazi paramilitary militia" by Conyers and Yoho. Some members of the battalion are openly white supremacists.

Academic use of the term

The term white supremacy is used in some academic studies of racial power to denote a system of structural or societal racism which privileges white people over others, regardless of the presence or the absence of racial hatred. White racial advantages occur at both a collective and an individual level (ceteris paribus, i. e., when individuals are compared that do not relevantly differ except in ethnicity). Legal scholar Frances Lee Ansley explains this definition as follows:

By "white supremacy" I do not mean to allude only to the self-conscious racism of white supremacist hate groups. I refer instead to a political, economic and cultural system in which whites overwhelmingly control power and material resources, conscious and unconscious ideas of white superiority and entitlement are widespread, and relations of white dominance and non-white subordination are daily reenacted across a broad array of institutions and social settings.

This and similar definitions have been adopted or proposed by Charles Mills, bell hooks, David Gillborn, Jessie Daniels, and Neely Fuller Jr, and they are widely used in critical race theory and intersectional feminism. Some anti-racist educators, such as Betita Martinez and the Challenging White Supremacy workshop, also use the term in this way. The term expresses historic continuities between a pre–civil rights movement era of open white supremacism and the current racial power structure of the United States. It also expresses the visceral impact of structural racism through "provocative and brutal" language that characterizes racism as "nefarious, global, systemic, and constant". Academic users of the term sometimes prefer it to racism because it allows for a distinction to be drawn between racist feelings and white racial advantage or privilege.

The term's recent rise in popularity among leftist activists has been characterized by some as counterproductive. John McWhorter, a specialist in language and race relations, has described its use as straying from its commonly accepted meaning to encompass less extreme issues, thereby cheapening the term and potentially derailing productive discussion. Political columnist Kevin Drum attributes the term's growing popularity to frequent use by Ta-Nehisi Coates, describing it as a "terrible fad" which fails to convey nuance. He claims that the term should be reserved for those who are trying to promote the idea that whites are inherently superior to blacks and not used to characterize less blatantly racist beliefs or actions. The use of the academic definition of white supremacy has been criticized by Conor Friedersdorf for the confusion it creates for the general public inasmuch as it differs from the more common dictionary definition; he argues that it is likely to alienate those it hopes to convince.

Ideologies and movements

Supporters of Nordicism consider the "Nordic peoples" to be a superior race. By the early 19th century, white supremacy was attached to emerging theories of racial hierarchy. The German philosopher Arthur Schopenhauer attributed cultural primacy to the white race:

The highest civilization and culture, apart from the ancient Hindus and Egyptians, are found exclusively among the white races; and even with many dark peoples, the ruling caste or race is fairer in colour than the rest and has, therefore, evidently immigrated, for example, the Brahmans, the Incas, and the rulers of the South Sea Islands. All this is due to the fact that necessity is the mother of invention because those tribes that emigrated early to the north, and there gradually became white, had to develop all their intellectual powers and invent and perfect all the arts in their struggle with need, want and misery, which in their many forms were brought about by the climate.

The Good Citizen 1926, published by Pillar of Fire Church

 

The eugenicist Madison Grant argued in his 1916 book, The Passing of the Great Race, that the Nordic race had been responsible for most of humanity's great achievements, and that admixture was "race suicide". In this book, Europeans who are not of Germanic origin but have Nordic characteristics such as blonde/red hair and blue/green/gray eyes, were considered to be a Nordic admixture and suitable for Aryanization.

Members of the second Ku Klux Klan at a rally in 1923.

 

In the United States, the Ku Klux Klan (KKK) is the group most associated with the white supremacist movement. Many white supremacist groups are based on the concept of preserving genetic purity, and do not focus solely on discrimination based on skin color. The KKK's reasons for supporting racial segregation are not primarily based on religious ideals, but some Klan groups are openly Protestant. The KKK and other white supremacist groups like Aryan Nations, The Order and the White Patriot Party are considered antisemitic.

Nazi Germany promulgated white supremacy based on the belief that the Aryan race, or the Germans, were the master race. It was combined with a eugenics programme that aimed for racial hygiene through compulsory sterilization of sick individuals and extermination of Untermenschen ("subhumans"): Slavs, Jews and Romani, which eventually culminated in the Holocaust.

Christian Identity is another movement closely tied to white supremacy. Some white supremacists identify themselves as Odinists, although many Odinists reject white supremacy. Some white supremacist groups, such as the South African Boeremag, conflate elements of Christianity and Odinism. Creativity (formerly known as "The World Church of the Creator") is atheistic and it denounces Christianity and other theistic religions. Aside from this, its ideology is similar to that of many Christian Identity groups because it believes in the antisemitic conspiracy theory that there is a "Jewish conspiracy" in control of governments, the banking industry and the media. Matthew F. Hale, founder of the World Church of the Creator, has published articles stating that all races other than white are "mud races", which is what the group's religion teaches.

The white supremacist ideology has become associated with a racist faction of the skinhead subculture, despite the fact that when the skinhead culture first developed in the United Kingdom in the late 1960s, it was heavily influenced by black fashions and music, especially Jamaican reggae and ska, and African American soul music.

White supremacist recruitment activities are primarily conducted at a grassroots level as well as on the Internet. Widespread access to the Internet has led to a dramatic increase in white supremacist websites. The Internet provides a venue to openly express white supremacist ideas at little social cost, because people who post the information are able to remain anonymous.

White separatism

White separatism is a political and social movement that seeks the separation of white people from people of other races and ethnicities, the establishment of a white ethnostate by removing non-whites from existing communities or by forming new communities elsewhere.

Most modern researchers view that white separatism is not distinct from white supremacist beliefs. The Anti-Defamation League defines white separatism as "a form of white supremacy"; the Southern Poverty Law Center defines both white nationalism and white separatism as "ideologies based on white supremacy." Facebook has banned content that is openly white nationalist or white separatist because "white nationalism and white separatism cannot be meaningfully separated from white supremacy and organized hate groups".

Use of the term to self-identify has been criticized as a dishonest rhetorical ploy. The Anti-Defamation League argues that white supremacists use the phrase because they believe it has fewer negative connotations than the term white supremacist.

Dobratz & Shanks-Meile reported that adherents usually reject marriage "outside the white race". They argued the existence of "a distinction between the white supremacist's desire to dominate (as in apartheid, slavery, or segregation) and complete separation by race". They argued that this is a matter of pragmatism, that while many white supremacists are also white separatists, contemporary white separatists reject the view that returning to a system of segregation is possible or desirable in the United States.