Since the 1950s, in different administrative and organizational forms, the United States' Food for Peace
program has used America's agricultural surpluses to provide food
assistance around the world, broaden international trade, and advance
U.S. international diplomacy. Approximately 4 billion people in 150
countries have benefited directly from U.S. food assistance.
The Bureau for Humanitarian Assistance within the United States Agency for International Development (USAID) is the U.S. Government's largest provider of overseas food assistance.
The food assistance programming is funded primarily through the Food
for Peace Act. The Bureau for Humanitarian Assistance also receives
International Disaster Assistance Funds through the Foreign Assistance Act (FAA) that can be used in emergency settings (more information below).
While U.S. food aid started out in the 1950s by donating surplus
U.S. commodities to nations in need, the U.S. now purchases food for
donation directly from American farmers through a competitive process.
The Bureau for Humanitarian Assistance identifies need in close
consultation with the host government requesting the assistance.
During the 2010s the program underwent revisions offered by in the Administration's Fiscal Year 2014 budget.
These revisions would change the program to provide cash donations
rather than American grown and delivered food. On April 24, 2013, the
chairman of USA Maritime,
a coalition of carriers and maritime unions, wrote a statement which
discussed the efficacy of the program and specifically the importance of
the U.S. Merchant Marine in delivering the U.S. food aid to people who
are undernourished around the world. Henry cited the fact that USAID's
own data actually revealed that the traditional efforts to deliver food
as opposed to cash transfers for countries to buy their own food is
actually 78 percent cheaper per ton of food. Henry offers that this is a
significant fact in the effort to address global hunger.
Early history of United States food assistance
America's food assistance programs began in 1812 when James Madison sent emergency aid to earthquake victims in Venezuela. As director of the American Relief Administration, Herbert Hoover led a $20 million feeding program in Russia during the 1920s under the Russian Famine Relief Act. In 1948, the United States launched the Marshall Plan,
which provided dollars for Europeans to purchase American food exports.
The Marshall Plan helped rejuvenate and unite Europe while laying the
foundations for a permanent U.S. food assistance program. Many of the
European countries the U.S. Government helped at that time have since
become major food exporters and important international donors.
Authorizing legislation
Public Law 480 (1954)
Minnesota Senator Hubert Humphrey,
a leading liberal Democrat, promoted a food for peace program that
would give away surplus crops owned by the U.S. government as an
instrument of foreign policy in the Cold War. The bill appealed to some
conservative Republicans from farm states, but was opposed by others,
including Barry Goldwater.
Another account credits the idea to Cheyenne County, Kansas farmer Peter O'Brien, who shared the idea, in 1953, while attending a local Farm Bureau meeting. (At the time, U.S. agricultural surpluses had reached "alarming levels," according to the Robert J. Dole Institute of Politics,
and storing the "excess grain" was costing the government "millions of
dollars" annually — while it "deteriorated and became inedible.") A U.S.
Senator from Kansas, Andy Schoeppel, sponsored such legislation.
On July 10, 1954, Dwight D. Eisenhower, another Kansan, signed the Agricultural Trade Development and Assistance Act
— or Public Law (P.L.) 480 — an action which simultaneously created the
Office of Food for Peace. By signing this legislation, the President
laid "the basis for a permanent expansion of our exports of agricultural
products with lasting benefits to ourselves and peoples of other
lands." The bill, a solution for food deficient, cash-poor countries,
created a secondary foreign market by allowing food-deficient countries
to pay for American food imports in their own currencies instead of in
U.S. dollars. These currencies were, for the most part, worthless
outside their issuing countries. The U.S. used these currencies to pay
for economic development projects inside those countries.
The law's original purpose was to expand international trade, to
promote the economic stability of American agriculture, to make maximum
use of surplus agricultural commodities in the furtherance of foreign
policy, and to stimulate the expansion of foreign trade in agricultural
commodities produced in the United States. Critics view the law as "a means of disposing of costly domestic agricultural surpluses."
The law was originally drafted by future Foreign Agricultural Service (FAS) administrator Gwynn Garnett after returning from a trip to India
in 1950. The bill is unusual in that it gave the FAS the ability to
conclude agreements with foreign governments without the approval of the
United States Senate.
Lyndon B. Johnson
limited the PL-480 grain shipments for critical famine aid to India, to
pressure it into toning down its criticism on the US involvement in the Vietnam War.
Kennedy era and Food for Peace Act (1966)
George McGovern as Food for Peace director in 1961, with President John F. Kennedy
In 1961, President John F. Kennedy
termed the law "Food for Peace," stating, "Food is strength, and food
is peace, and food is freedom, and food is a helping hand to people
around the world whose good will and friendship we want."
Through new amendments, the law switched its focus from disposing of
surplus agricultural commodities to addressing humanitarian needs and
responding to growing food crisis demands. In signing the extension of
the Agricultural Trade Development and Assistance Act in 1959, President
Eisenhower criticized the shortcomings of the amendment. He
specifically referred to the extension as the Food for Peace program.
Although Kennedy may have expanded the program, he was not the first to
refer to the program as Food for Peace.
Former U.S. Representative from South Dakota George McGovern
was picked to become a Special Assistant to the President and first
director of Kennedy's high-priority Food for Peace program, which
realized what McGovern had been advocating in the House. McGovern assumed the post on January 21, 1961.
As director, McGovern urged the greater use of food to enable
foreign economic development, saying, "We should thank God that we have a
food abundance and use the over-supply among the under-privileged at
home and abroad." He found space for the program in the Executive Office Building rather than be subservient to either the U.S. Department of State or U.S. Department of Agriculture. McGovern worked with deputy director James W. Symington and Kennedy advisor Arthur M. Schlesinger, Jr. in visiting South America to discuss surplus grain distribution, and attended meetings of the United Nations' Food and Agriculture Organization.
By the close of 1961, the Food for Peace program was operating in a dozen countries, and 10 million more people had been fed with American surplus than the year before. In February 1962, McGovern visited India and oversaw a greatly expanded school lunch program thanks to Food for Peace; subsequently one in five Indian schoolchildren would be fed from it, and by mid-1962, 35 million children around the world. During an audience in Rome, Pope John XXIII warmly praised McGovern's work.
McGovern resigned his post on July 18, 1962, wanting to resume his electoral political career.Kennedy said that under McGovern, the program had "become a vital force
in the world", improving living conditions and economies of allies and
creating "a powerful barrier to the spread of Communism". Columnist Drew Pearson wrote that it was one of the "most spectacular achievements of the young Kennedy administration," while Schlesinger would later write that Food for Peace had been "the greatest unseen weapon of Kennedy's third-world policy".
McGovern was succeeded by Richard W. Reuter, who had been the executive director of CARE. In 1965, during the Lyndon B. Johnson administration, the program was folded into the State Department under Secretary Dean Rusk.
A year later Reuther resigned his retitled position of Special
Assistant to the Secretary of State for Food for Peace, reportedly
dismayed by the direction the food program had taken.
The Food for Peace Act of 1966, P.L. 89-808, 80 Stat.1526,
revised the basic structure of the programs and placed the emphasis
clearly on the humanitarian goals of the program. The policy statement
shifted from surplus disposal to planned production for export to meet
world food needs.
Food, Agriculture, Conservation, and Trade Act (1990)
In 1990, the U.S. Congress passed, and President George H. W. Bush signed into law the first comprehensive restatement and reorganization of P.L. 480 in the Food, Agriculture, Conservation and Trade Act
(the 1990 Farm Bill). This bill made a significant change in the
overall focus of P.L. 480. Once seen as simply an aspect of foreign
policy, P.L. 480 now has food security as a primary goal.
Food for Peace Act (2008)
In 2008, the Food for Peace Act, (Pub. L.110–246 (text)(PDF)) formally replaced the Agricultural Trade Development and Assistance Act. Programs are authorized, along with all U.S. agricultural programs, through the Farm Bill which Congress typically amends and reauthorizes every five years.
Provisions
The purpose of the Food for Peace Act is to:
Combat world hunger and malnutrition and their causes
Promote broad-based, equitable and sustainable development, including agricultural development
Expand international trade
Foster and encourage the development of private enterprise and democratic participation in developing countries
Prevent conflicts
The Food for Peace Act includes four sections, referred to as titles,
which regulate food aid commodities and development and relief support.
The United States Department of Agriculture (USDA) manages Title I, while USAID manages Titles II, III and V.
Title I: Economic Assistance and Food Security—governs concessional sales of U.S. agricultural commodities to developing countries and private entities
Title II: Emergency and Private Assistance Programs—provide for the direct donation of U.S. agricultural commodities for emergency relief and development programs
Title III: Food for Development—provides government-to-government grants of agricultural commodities, which are tied to policy reform
Title IV: General Authorities and Requirements – establishes
prohibited uses including no aid to human rights violators, no aid to
military, and no competition with U.S. producers
Title V: John Ogonowski and Doug Bereuter Farmer-to-Farmer (FTF) Program—-provides voluntary technical assistance to farmers, farm groups, and agribusinesses.
Title VI: Enterprise for the America's Initiative – official
debt relief linking Food for Peace and AID debt owed to the United
States to the promulgation of structural adjustment and open investment
policies
Title I: Economic Assistance and Food Security (USDA)
The
Title I authority of the Food for Peace Act is administered by the U.S.
Department of Agriculture (USDA) and provides funding for a
concessional sales program and the Food for Progress grant program.
The concessional sales program supports trade and development.
The primary objective of the concessional sales component is to provide
food assistance to targeted developing countries to promote economic
growth. The 1996 Farm Bill modified Title I concessional loans to allow
USDA to enter into loan agreements with private entities in addition to
its government-to-government mandate. As a result, the new goal of the
Title I program was to prioritize areas that had the potential to become
commercial markets for U.S. agricultural commodities.
Food for Progress authorizes the Commodity Credit Corporation
(CCC) to finance the sale and export of agricultural commodities to
development countries and emerging democracies on credit terms, or on a
grant basis, to support developing countries and countries that are
emerging democracies and have made commitments to introduce or expand
free enterprise elements into their agricultural economies.
Since fiscal year 2006, new funding has not been requested
because demand for food assistance using credit financing has fallen or
grant programs have been a more appropriate tool.
Title II: Emergency and Development Food Assistance Programs (USAID)
Title II is administered by the USAID Office of Food for Peace as authorized in the Food for Peace Act which states
the Administrator may provide agricultural commodities to
meet emergency food needs under this title through governments and
public or private agencies […] The Administrator may provide
agricultural commodities for nonemergency assistance under this title
through eligible organizations.
It authorizes use of U.S. agricultural commodities for both emergency and development food assistance programs to:
Address famine or other urgent relief requirements
Combat malnutrition
Alleviate the causes of hunger, mortality, and morbidity
Promote economic and community development
Promote sound environmental practices
Carry out feeding programs
Title II emergency and development programs have provided more than
106 million metric tons of commodities to more than 3 billion people in
150 countries. Title II programs respond to emergencies and focus on
reducing food insecurity in vulnerable populations as well as improving
resilience to shocks, by incorporating many activities to strengthen
local capacity to prevent and respond to natural disasters.
Since 2011, the Office of Food for Peace has begun work to
reformulate its food commodities to make them more nutritious. These
reformulated products are used for both emergency and development
programs.
Title III: Food for Development (USAID)
The
Food for Peace Title III program is a USAID-administered tool for
enhancing food security and supporting long-term economic development in
the least-developed countries. When funded, the USG donates
agricultural commodities to the recipient country and funds their
transportation to the point of entry in the recipient country. These
commodities are sold on the domestic market and the revenue generated
from their sale is used to support and implement economic development
and food security programs.
Funds were last requested or appropriated for Title III before 2000.
Title IV: General Authorities and Requirements
Title
IV of the Food for Peace Act authorizes active participation of the
private sector in storage, marketing, transport and distribution. It
requires multi-year agreements and an annual report to Congress. Title
IV also contains debt forgiveness provisions and establishes the
prohibited uses of food aid, which are:
No aid to human rights violators (can be waived in emergency situations)
No aid to military
No competition with U.S. producers
Title V: John Ogonowski and Doug Bereuter Farmer-to-Farmer (F2F) Program (USAID)
Title V funds the Farmer-to-Farmer Program which was authorized in the Food Security Act of 1985.
The U.S. Congress authorized the FY 2008-2012 phase of the
Farmer-to-Farmer Program in the 2008 Food for Peace Act, designating it
the "John Ogonowski and Doug Bereuter Farmer-to-Farmer Program" in honor
of Ogonowski, one of the pilots killed on September 11, 2001, and
former Congressman Bereuter, who initially sponsored the program.
The Farmer-to-Farmer Program provides voluntary technical
assistance to farmers, farm groups and agribusinesses in developing and
transitional countries to promote sustainable improvements in food
processing, production and marketing. The program relies on the
expertise of volunteers from U.S. farms, land grant universities,
cooperatives, private agribusinesses and nonprofit farm organizations to
respond to the needs of host-country farmers and organizations.
Title VI: Enterprise for the America's Initiative
Title
VI of the Food for Peace Act authorizes official debt relief. It links
Food for Peace and AID debt owed to the United States to the
promulgation of structural adjustment and open investment policies.
Title VI is administered by the Department of the Treasury.
Related legislation
Food for Progress Act of 1985—allows
for commodity donations to be available to emerging democracies and
developing countries committed to the introduction or expansion of free
enterprise in their agricultural economies.
Section 416 of the Agricultural Act of 1949—establishes the
McGovern-Dole International Food for Education and Child Nutrition
Program which consists of donations of U.S. agricultural products, as
well as financial and technical assistance, for school feeding and
maternal and child nutrition projects in low-income countries. It also
provides for overseas donations of surplus food and feed grain owned by
the USDA Commodity Credit Corporation (CCC).
Africa: Seeds of Hope Act of 1988: Bill Emerson Humanitarian Trust—creates
a food reserve administered under the authority of the Secretary of
Agriculture. This reserve is available to meet emergency humanitarian
food needs in developing countries, allowing the United States to
respond to unanticipated food crises. Under the 2008 Food for Peace Act,
the Administrator of USAID oversees release and use of these funds.
Food for Peace programs
Emergency programs
USAID's
Office of Food for Peace manages two programs to support emergency food
assistance efforts. Emergency programs authorized under Title II of the
Food for Peace Act provide in-kind commodities and associated costs.
Emergency programs implemented by Food for Peace using International
Disaster Assistance Funds (called the Emergency Food Security Program,
or EFSP) provide cash that can be used for local and regional purchase
of food and other interventions such as food vouchers and cash
transfers. Title II is authorized by the Food for Peace Act, while EFSP
is authorized under the Foreign Assistance Act
(FAA). EFSP is deployed to respond to the highest priority emergency
food security needs as a complement to Title II in-kind food aid. Both
programs provide emergency food assistance to address needs arising from
natural disasters, such as floods or droughts, and complex emergencies,
which are often characterized by insecurity and population
displacement.
Development programs
The
Office of Food for Peace manages development food assistance programs
through Title II of the Food for Peace Act, which target the underlying
causes of hunger and malnutrition, including interventions in health and
nutrition, agriculture, and water and sanitation, among others. These
programs focus on approximately 20 priority countries determined based
on the weighted average of the country ranking under three food security
indicators:
Percent of children stunted
Percent of population living on less than $1.25 per day
Percent of population undernourished
Additional considerations such as security conditions also factor into countries selected.
International Food Relief Partnership (IFRP)
The
International Food Relief Partnership (IFRP) is a sub-program of Title
II food assistance. IFRP provides small grants to predominantly
faith-based groups working on nutritional support programs. IFRP allows
for the transportation, delivery, and distribution of shelf-stable
prepackaged foods overseas and the establishment and maintenance of
stockpiles of the foods in the United States.
Famine Early Warning Systems Network (FEWS NET)
USAID's
Famine Early Warning Systems Network (FEWS NET) works with other U.S.
government agencies to monitor, collect, analyze and disseminate
critical data and information on conditions of food availability and
access in the most food insecure countries. These agencies include the
U.S. Geological Survey, National Aeronautics and Space Administration
(NASA), National Oceanic and Atmospheric Administration, and U.S.
Department of Agriculture. FEWS NET provides decision-makers in the U.S.
Government, host country governments, and a variety of other regional
and international partners timely, unbiased, and insightful early
warning and vulnerability information.
https://en.wikipedia.org/wiki/Genetics Genetics is the study of genes, genetic variation, and heredity in organisms. It is an important branch in biology because heredity is vital to organisms' evolution. Gregor Mendel, a MoravianAugustinian friar working in the 19th century in Brno,
was the first to study genetics scientifically. Mendel studied "trait
inheritance", patterns in the way traits are handed down from parents to
offspring over time. He observed that organisms (pea plants) inherit
traits by way of discrete "units of inheritance". This term, still used
today, is a somewhat ambiguous definition of what is referred to as a
gene.
Trait inheritance and molecular
inheritance mechanisms of genes are still primary principles of
genetics in the 21st century, but modern genetics has expanded to study
the function and behavior of genes. Gene structure and function,
variation, and distribution are studied within the context of the cell, the organism (e.g. dominance), and within the context of a population. Genetics has given rise to a number of subfields, including molecular genetics, epigenetics, and population genetics. Organisms studied within the broad field span the domains of life (archaea, bacteria, and eukarya).
Genetic processes work in combination with an organism's environment and experiences to influence development and behavior, often referred to as nature versus nurture. The intracellular or extracellular
environment of a living cell or organism may increase or decrease gene
transcription. A classic example is two seeds of genetically identical
corn, one placed in a temperate climate and one in an arid climate
(lacking sufficient waterfall or rain). While the average height the
two corn stalks could grow to is genetically determined, the one in the
arid climate only grows to half the height of the one in the temperate
climate due to lack of water and nutrients in its environment.
Etymology
The word genetics stems from the ancient Greekγενετικόςgenetikos meaning "genitive"/"generative", which in turn derives from γένεσιςgenesis meaning "origin".
The observation that living things inherit traits from their parents has been used since prehistoric times to improve crop plants and animals through selective breeding. The modern science of genetics, seeking to understand this process, began with the work of the Augustinian friar Gregor Mendel in the mid-19th century.
Prior to Mendel, Imre Festetics, a Hungarian
noble, who lived in Kőszeg before Mendel, was the first who used the
word "genetic" in hereditarian context, and is considered the first
geneticist. He described several rules of biological inheritance in his
work The genetic laws of nature (Die genetischen Gesetze der Natur, 1819). His second law is the same as that which Mendel published. In his third law, he developed the basic principles of mutation (he can be considered a forerunner of Hugo de Vries). Festetics argued that changes observed in the generation of farm animals, plants, and humans are the result of scientific laws.
Festetics empirically deduced that organisms inherit their
characteristics, not acquire them. He recognized recessive traits and
inherent variation by postulating that traits of past generations could
reappear later, and organisms could produce progeny with different
attributes.
These observations represent an important prelude to Mendel's theory of
particulate inheritance insofar as it features a transition of heredity
from its status as myth to that of a scientific discipline, by
providing a fundamental theoretical basis for genetics in the twentieth
century.
Other theories of inheritance preceded Mendel's work. A popular theory during the 19th century, and implied by Charles Darwin's 1859 On the Origin of Species, was blending inheritance: the idea that individuals inherit a smooth blend of traits from their parents.
Mendel's work provided examples where traits were definitely not
blended after hybridization, showing that traits are produced by
combinations of distinct genes rather than a continuous blend. Blending
of traits in the progeny is now explained by the action of multiple
genes with quantitative effects. Another theory that had some support at that time was the inheritance of acquired characteristics: the belief that individuals inherit traits strengthened by their parents. This theory (commonly associated with Jean-Baptiste Lamarck) is now known to be wrong—the experiences of individuals do not affect the genes they pass to their children. Other theories included Darwin's pangenesis (which had both acquired and inherited aspects) and Francis Galton's reformulation of pangenesis as both particulate and inherited.
Mendelian genetics
Morgan's observation of sex-linked inheritance of a mutation causing white eyes in Drosophila led him to the hypothesis that genes are located upon chromosomes.
Modern genetics started with Mendel's studies of the nature of inheritance in plants. In his paper "Versuche über Pflanzenhybriden" ("Experiments on Plant Hybridization"), presented in 1865 to the Naturforschender Verein (Society for Research in Nature) in Brno,
Mendel traced the inheritance patterns of certain traits in pea plants
and described them mathematically. Although this pattern of inheritance
could only be observed for a few traits, Mendel's work suggested that
heredity was particulate, not acquired, and that the inheritance
patterns of many traits could be explained through simple rules and
ratios.
The importance of Mendel's work did not gain wide understanding until 1900, after his death, when Hugo de Vries and other scientists rediscovered his research. William Bateson, a proponent of Mendel's work, coined the word genetics in 1905. The adjective genetic, derived from the Greek word genesis—γένεσις, "origin", predates the noun and was first used in a biological sense in 1860.
Bateson both acted as a mentor and was aided significantly by the work
of other scientists from Newnham College at Cambridge, specifically the
work of Becky Saunders, Nora Darwin Barlow, and Muriel Wheldale Onslow. Bateson popularized the usage of the word genetics to describe the study of inheritance in his inaugural address to the Third International Conference on Plant Hybridization in London in 1906.
After the rediscovery of Mendel's work, scientists tried to
determine which molecules in the cell were responsible for inheritance.
In 1900, Nettie Stevens began studying the mealworm. Over the next 11 years, she discovered that females only had the X chromosome and males had both X and Y chromosomes. She was able to conclude that sex is a chromosomal factor and is determined by the male. In 1911, Thomas Hunt Morgan argued that genes are on chromosomes, based on observations of a sex-linked white eye mutation in fruit flies. In 1913, his student Alfred Sturtevant used the phenomenon of genetic linkage to show that genes are arranged linearly on the chromosome.
DNA, the molecular basis for biological inheritance. Each strand of DNA is a chain of nucleotides, matching each other in the center to form what look like rungs on a twisted ladder.
Although genes were known to exist on chromosomes, chromosomes are composed of both protein and DNA, and scientists did not know which of the two is responsible for inheritance. In 1928, Frederick Griffith discovered the phenomenon of transformation: dead bacteria could transfer genetic material to "transform" other still-living bacteria. Sixteen years later, in 1944, the Avery–MacLeod–McCarty experiment identified DNA as the molecule responsible for transformation. The role of the nucleus as the repository of genetic information in eukaryotes had been established by Hämmerling in 1943 in his work on the single celled alga Acetabularia. The Hershey–Chase experiment
in 1952 confirmed that DNA (rather than protein) is the genetic
material of the viruses that infect bacteria, providing further evidence
that DNA is the molecule responsible for inheritance.
James Watson and Francis Crick determined the structure of DNA in 1953, using the X-ray crystallography work of Rosalind Franklin and Maurice Wilkins that indicated DNA has a helical structure (i.e., shaped like a corkscrew).
Their double-helix model had two strands of DNA with the nucleotides
pointing inward, each matching a complementary nucleotide on the other
strand to form what look like rungs on a twisted ladder.
This structure showed that genetic information exists in the sequence
of nucleotides on each strand of DNA. The structure also suggested a
simple method for replication:
if the strands are separated, new partner strands can be reconstructed
for each based on the sequence of the old strand. This property is what
gives DNA its semi-conservative nature where one strand of new DNA is
from an original parent strand.
Although the structure of DNA showed how inheritance works, it
was still not known how DNA influences the behavior of cells. In the
following years, scientists tried to understand how DNA controls the
process of protein production. It was discovered that the cell uses DNA as a template to create matching messenger RNA, molecules with nucleotides very similar to DNA. The nucleotide sequence of a messenger RNA is used to create an amino acid sequence in protein; this translation between nucleotide sequences and amino acid sequences is known as the genetic code.
With the newfound molecular understanding of inheritance came an explosion of research. A notable theory arose from Tomoko Ohta in 1973 with her amendment to the neutral theory of molecular evolution through publishing the nearly neutral theory of molecular evolution. In this theory, Ohta stressed the importance of natural selection and the environment to the rate at which genetic evolution occurs. One important development was chain-termination DNA sequencing in 1977 by Frederick Sanger. This technology allows scientists to read the nucleotide sequence of a DNA molecule. In 1983, Kary Banks Mullis developed the polymerase chain reaction, providing a quick way to isolate and amplify a specific section of DNA from a mixture. The efforts of the Human Genome Project, Department of Energy, NIH, and parallel private efforts by Celera Genomics led to the sequencing of the human genome in 2003.
A Punnett square depicting a cross between two pea plants heterozygous for purple (B) and white (b) blossoms
At its most fundamental level, inheritance in organisms occurs by passing discrete heritable units, called genes, from parents to offspring. This property was first observed by Gregor Mendel, who studied the segregation of heritable traits in pea
plants, showing for example that flowers on a single plant were either
purple or white—but never an intermediate between the two colors. The
discrete versions of the same gene controlling the inherited appearance
(phenotypes) are called alleles.
In the case of the pea, which is a diploid species, each individual plant has two copies of each gene, one copy inherited from each parent.
Many species, including humans, have this pattern of inheritance.
Diploid organisms with two copies of the same allele of a given gene are
called homozygous at that gene locus, while organisms with two different alleles of a given gene are called heterozygous. The set of alleles for a given organism is called its genotype, while the observable traits of the organism are called its phenotype. When organisms are heterozygous at a gene, often one allele is called dominant as its qualities dominate the phenotype of the organism, while the other allele is called recessive as its qualities recede and are not observed. Some alleles do not have complete dominance and instead have incomplete dominance by expressing an intermediate phenotype, or codominance by expressing both alleles at once.
When a pair of organisms reproduce sexually,
their offspring randomly inherit one of the two alleles from each
parent. These observations of discrete inheritance and the segregation
of alleles are collectively known as Mendel's first law
or the Law of Segregation. However, the probability of getting one gene
over the other can change due to dominant, recessive, homozygous, or
heterozygous genes. For example, Mendel found that if you cross
heterozygous organisms your odds of getting the dominant trait is 3:1.
Real geneticist study and calculate probabilities by using theoretical
probabilities, empirical probabilities, the product rule, the sum rule,
and more.
Notation and diagrams
Genetic pedigree charts help track the inheritance patterns of traits.
Geneticists use diagrams and symbols to describe inheritance. A gene
is represented by one or a few letters. Often a "+" symbol is used to
mark the usual, non-mutant allele for a gene.
In fertilization and breeding experiments (and especially when
discussing Mendel's laws) the parents are referred to as the "P"
generation and the offspring as the "F1" (first filial) generation. When
the F1 offspring mate with each other, the offspring are called the
"F2" (second filial) generation. One of the common diagrams used to
predict the result of cross-breeding is the Punnett square.
When studying human genetic diseases, geneticists often use pedigree charts to represent the inheritance of traits. These charts map the inheritance of a trait in a family tree.
Multiple gene interactions
Human height is a trait with complex genetic causes. Francis Galton's data from 1889 shows the relationship between offspring height as a function of mean parent height.
Organisms have thousands of genes, and in sexually reproducing
organisms these genes generally assort independently of each other. This
means that the inheritance of an allele for yellow or green pea color
is unrelated to the inheritance of alleles for white or purple flowers.
This phenomenon, known as "Mendel's second law"
or the "law of independent assortment," means that the alleles of
different genes get shuffled between parents to form offspring with many
different combinations. Different genes often interact to influence the
same trait. In the Blue-eyed Mary (Omphalodes verna),
for example, there exists a gene with alleles that determine the color
of flowers: blue or magenta. Another gene, however, controls whether the
flowers have color at all or are white. When a plant has two copies of
this white allele, its flowers are white—regardless of whether the first
gene has blue or magenta alleles. This interaction between genes is
called epistasis, with the second gene epistatic to the first.
Many traits are not discrete features (e.g. purple or white flowers) but are instead continuous features (e.g. human height and skin color). These complex traits are products of many genes.
The influence of these genes is mediated, to varying degrees, by the
environment an organism has experienced. The degree to which an
organism's genes contribute to a complex trait is called heritability.
Measurement of the heritability of a trait is relative—in a more
variable environment, the environment has a bigger influence on the
total variation of the trait. For example, human height is a trait with
complex causes. It has a heritability of 89% in the United States. In
Nigeria, however, where people experience a more variable access to good
nutrition and health care, height has a heritability of only 62%.
The molecular basis for genes is deoxyribonucleic acid (DNA). DNA is composed of deoxyribose (sugar molecule), a phosphate group, and a base (amine group). There are four types of bases: adenine (A), cytosine (C), guanine (G), and thymine
(T). The phosphates make phosphodiester bonds with the sugars to make
long phosphate-sugar backbones. Bases specifically pair together
(T&A, C&G) between two backbones and make like rungs on a
ladder. The bases, phosphates, and sugars together make a nucleotide that connects to make long chains of DNA. Genetic information exists in the sequence of these nucleotides, and genes exist as stretches of sequence along the DNA chain. These chains coil into a double a-helix structure and wrap around proteins called Histones which provide the structural support. DNA wrapped around these histones are called chromosomes. Viruses sometimes use the similar molecule RNA instead of DNA as their genetic material.
DNA normally exists as a double-stranded molecule, coiled into the shape of a double helix.
Each nucleotide in DNA preferentially pairs with its partner nucleotide
on the opposite strand: A pairs with T, and C pairs with G. Thus, in
its two-stranded form, each strand effectively contains all necessary
information, redundant with its partner strand. This structure of DNA is
the physical basis for inheritance: DNA replication duplicates the
genetic information by splitting the strands and using each strand as a
template for synthesis of a new partner strand.
Genes are arranged linearly along long chains of DNA base-pair sequences. In bacteria, each cell usually contains a single circular genophore, while eukaryotic
organisms (such as plants and animals) have their DNA arranged in
multiple linear chromosomes. These DNA strands are often extremely long;
the largest human chromosome, for example, is about 247 million base pairs in length.
The DNA of a chromosome is associated with structural proteins that
organize, compact, and control access to the DNA, forming a material
called chromatin; in eukaryotes, chromatin is usually composed of nucleosomes, segments of DNA wound around cores of histone proteins. The full set of hereditary material in an organism (usually the combined DNA sequences of all chromosomes) is called the genome.
DNA is most often found in the nucleus of cells, but Ruth Sager
helped in the discovery of nonchromosomal genes found outside of the
nucleus. In plants, these are often found in the chloroplasts and in other organisms, in the mitochondria.
These nonchromosomal genes can still be passed on by either partner in
sexual reproduction and they control a variety of hereditary
characteristics that replicate and remain active throughout generations.
While haploid organisms have only one copy of each chromosome, most animals and many plants are diploid, containing two of each chromosome and thus two copies of every gene. The two alleles for a gene are located on identical loci of the two homologous chromosomes, each allele inherited from a different parent.
Many species have so-called sex chromosomes that determine the sex of each organism. In humans and many other animals, the Y chromosome
contains the gene that triggers the development of the specifically
male characteristics. In evolution, this chromosome has lost most of its
content and also most of its genes, while the X chromosome
is similar to the other chromosomes and contains many genes. This being
said, Mary Frances Lyon discovered that there is X-chromosome
inactivation during reproduction to avoid passing on twice as many genes
to the offspring. Lyon's discovery led to the discovery of X-linked diseases.
Walther Flemming's
1882 diagram of eukaryotic cell division. Chromosomes are copied,
condensed, and organized. Then, as the cell divides, chromosome copies
separate into the daughter cells.
When cells divide, their full genome is copied and each daughter cell inherits one copy. This process, called mitosis,
is the simplest form of reproduction and is the basis for asexual
reproduction. Asexual reproduction can also occur in multicellular
organisms, producing offspring that inherit their genome from a single
parent. Offspring that are genetically identical to their parents are
called clones.
Eukaryotic
organisms often use sexual reproduction to generate offspring that
contain a mixture of genetic material inherited from two different
parents. The process of sexual reproduction alternates between forms
that contain single copies of the genome (haploid) and double copies (diploid).
Haploid cells fuse and combine genetic material to create a diploid
cell with paired chromosomes. Diploid organisms form haploids by
dividing, without replicating their DNA, to create daughter cells that
randomly inherit one of each pair of chromosomes. Most animals and many
plants are diploid for most of their lifespan, with the haploid form
reduced to single cell gametes such as sperm or eggs.
Although they do not use the haploid/diploid method of sexual reproduction, bacteria have many methods of acquiring new genetic information. Some bacteria can undergo conjugation, transferring a small circular piece of DNA to another bacterium.
Bacteria can also take up raw DNA fragments found in the environment
and integrate them into their genomes, a phenomenon known as transformation. These processes result in horizontal gene transfer, transmitting fragments of genetic information between organisms that would be otherwise unrelated. Natural bacterial transformation occurs in many bacterial species, and can be regarded as a sexual process for transferring DNA from one cell to another cell (usually of the same species). Transformation requires the action of numerous bacterial gene products, and its primary adaptive function appears to be repair of DNA damages in the recipient cell.
Thomas Hunt Morgan's 1916 illustration of a double crossover between chromosomes
The diploid nature of chromosomes allows for genes on different chromosomes to assort independently
or be separated from their homologous pair during sexual reproduction
wherein haploid gametes are formed. In this way new combinations of
genes can occur in the offspring of a mating pair. Genes on the same
chromosome would theoretically never recombine. However, they do, via
the cellular process of chromosomal crossover. During crossover, chromosomes exchange stretches of DNA, effectively shuffling the gene alleles between the chromosomes. This process of chromosomal crossover generally occurs during meiosis, a series of cell divisions that creates haploid cells. Meiotic recombination, particularly in microbial eukaryotes, appears to serve the adaptive function of repair of DNA damages.
The first cytological demonstration of crossing over was performed by Harriet Creighton and Barbara McClintock
in 1931. Their research and experiments on corn provided cytological
evidence for the genetic theory that linked genes on paired chromosomes
do in fact exchange places from one homolog to the other.
The probability of chromosomal crossover occurring between two
given points on the chromosome is related to the distance between the
points. For an arbitrarily long distance, the probability of crossover
is high enough that the inheritance of the genes is effectively
uncorrelated.
For genes that are closer together, however, the lower probability of
crossover means that the genes demonstrate genetic linkage; alleles for
the two genes tend to be inherited together. The amounts of linkage
between a series of genes can be combined to form a linear linkage map that roughly describes the arrangement of the genes along the chromosome.
Genes express
their functional effect through the production of proteins, which are
molecules responsible for most functions in the cell. Proteins are made
up of one or more polypeptide chains, each composed of a sequence of amino acids. The DNA sequence of a gene is used to produce a specific amino acid sequence. This process begins with the production of an RNA molecule with a sequence matching the gene's DNA sequence, a process called transcription.
This messenger RNA molecule then serves to produce a corresponding amino acid sequence through a process called translation. Each group of three nucleotides in the sequence, called a codon, corresponds either to one of the twenty possible amino acids in a protein or an instruction to end the amino acid sequence; this correspondence is called the genetic code.
The flow of information is unidirectional: information is transferred
from nucleotide sequences into the amino acid sequence of proteins, but
it never transfers from protein back into the sequence of DNA—a
phenomenon Francis Crick called the central dogma of molecular biology.
The specific sequence of amino acids results
in a unique three-dimensional structure for that protein, and the
three-dimensional structures of proteins are related to their functions. Some are simple structural molecules, like the fibers formed by the protein collagen. Proteins can bind to other proteins and simple molecules, sometimes acting as enzymes by facilitating chemical reactions within the bound molecules (without changing the structure of the protein itself). Protein structure is dynamic; the protein hemoglobin
bends into slightly different forms as it facilitates the capture,
transport, and release of oxygen molecules within mammalian blood.
A single nucleotide difference
within DNA can cause a change in the amino acid sequence of a protein.
Because protein structures are the result of their amino acid sequences,
some changes can dramatically change the properties of a protein by
destabilizing the structure or changing the surface of the protein in a
way that changes its interaction with other proteins and molecules. For
example, sickle-cell anemia is a human genetic disease that results from a single base difference within the coding region for the β-globin section of hemoglobin, causing a single amino acid change that changes hemoglobin's physical properties.
Sickle-cell versions of hemoglobin stick to themselves, stacking to form fibers that distort the shape of red blood cells carrying the protein. These sickle-shaped cells no longer flow smoothly through blood vessels, having a tendency to clog or degrade, causing the medical problems associated with this disease.
Some DNA sequences are transcribed into RNA but are not translated into protein products—such RNA molecules are called non-coding RNA. In some cases, these products fold into structures which are involved in critical cell functions (e.g. ribosomal RNA and transfer RNA). RNA can also have regulatory effects through hybridization interactions with other RNA molecules (such as microRNA).
Siamese cats have a temperature-sensitive pigment-production mutation.
Although genes contain all the information an organism uses to
function, the environment plays an important role in determining the
ultimate phenotypes an organism displays. The phrase "nature and nurture"
refers to this complementary relationship. The phenotype of an organism
depends on the interaction of genes and the environment. An interesting
example is the coat coloration of the Siamese cat.
In this case, the body temperature of the cat plays the role of the
environment. The cat's genes code for dark hair, thus the hair-producing
cells in the cat make cellular proteins resulting in dark hair. But
these dark hair-producing proteins are sensitive to temperature (i.e.
have a mutation causing temperature-sensitivity) and denature
in higher-temperature environments, failing to produce dark-hair
pigment in areas where the cat has a higher body temperature. In a
low-temperature environment, however, the protein's structure is stable
and produces dark-hair pigment normally. The protein remains functional
in areas of skin that are colder—such as its legs, ears, tail, and
face—so the cat has dark hair at its extremities.
Environment plays a major role in effects of the human genetic disease phenylketonuria. The mutation that causes phenylketonuria disrupts the ability of the body to break down the amino acid phenylalanine,
causing a toxic build-up of an intermediate molecule that, in turn,
causes severe symptoms of progressive intellectual disability and
seizures. However, if someone with the phenylketonuria mutation follows a
strict diet that avoids this amino acid, they remain normal and
healthy.
A common method for determining how genes and environment ("nature and nurture") contribute to a phenotype involves studying identical and fraternal twins, or other siblings of multiple births.
Identical siblings are genetically the same since they come from the
same zygote. Meanwhile, fraternal twins are as genetically different
from one another as normal siblings. By comparing how often a certain
disorder occurs in a pair of identical twins to how often it occurs in a
pair of fraternal twins, scientists can determine whether that disorder
is caused by genetic or postnatal environmental factors. One famous
example involved the study of the Genain quadruplets, who were identical quadruplets all diagnosed with schizophrenia.
The genome of a given organism contains thousands of genes, but not
all these genes need to be active at any given moment. A gene is
expressed when it is being transcribed into mRNA and there exist many
cellular methods of controlling the expression of genes such that
proteins are produced only when needed by the cell. Transcription factors are regulatory proteins that bind to DNA, either promoting or inhibiting the transcription of a gene. Within the genome of Escherichia coli bacteria, for example, there exists a series of genes necessary for the synthesis of the amino acid tryptophan.
However, when tryptophan is already available to the cell, these genes
for tryptophan synthesis are no longer needed. The presence of
tryptophan directly affects the activity of the genes—tryptophan
molecules bind to the tryptophan repressor
(a transcription factor), changing the repressor's structure such that
the repressor binds to the genes. The tryptophan repressor blocks the
transcription and expression of the genes, thereby creating negative feedback regulation of the tryptophan synthesis process.
Transcription factors bind to DNA, influencing the transcription of associated genes.
Differences in gene expression are especially clear within multicellular organisms,
where cells all contain the same genome but have very different
structures and behaviors due to the expression of different sets of
genes. All the cells in a multicellular organism derive from a single
cell, differentiating into variant cell types in response to external
and intercellular signals
and gradually establishing different patterns of gene expression to
create different behaviors. As no single gene is responsible for the development of structures within multicellular organisms, these patterns arise from the complex interactions between many cells.
Within eukaryotes, there exist structural features of chromatin
that influence the transcription of genes, often in the form of
modifications to DNA and chromatin that are stably inherited by daughter
cells. These features are called "epigenetic"
because they exist "on top" of the DNA sequence and retain inheritance
from one cell generation to the next. Because of epigenetic features,
different cell types grown
within the same medium can retain very different properties. Although
epigenetic features are generally dynamic over the course of
development, some, like the phenomenon of paramutation, have multigenerational inheritance and exist as rare exceptions to the general rule of DNA as the basis for inheritance.
Gene
duplication allows diversification by providing redundancy: one gene
can mutate and lose its original function without harming the organism.
During the process of DNA replication, errors occasionally occur in
the polymerization of the second strand. These errors, called mutations,
can affect the phenotype of an organism, especially if they occur
within the protein coding sequence of a gene. Error rates are usually
very low—1 error in every 10–100 million bases—due to the "proofreading"
ability of DNA polymerases. Processes that increase the rate of changes in DNA are called mutagenic: mutagenic chemicals promote errors in DNA replication, often by interfering with the structure of base-pairing, while UV radiation induces mutations by causing damage to the DNA structure. Chemical damage to DNA occurs naturally as well and cells use DNA repair
mechanisms to repair mismatches and breaks. The repair does not,
however, always restore the original sequence. A particularly important
source of DNA damages appears to be reactive oxygen species produced by cellular aerobic respiration, and these can lead to mutations.
In organisms that use chromosomal crossover
to exchange DNA and recombine genes, errors in alignment during meiosis
can also cause mutations. Errors in crossover are especially likely
when similar sequences cause partner chromosomes to adopt a mistaken
alignment; this makes some regions in genomes more prone to mutating in
this way. These errors create large structural changes in DNA sequence—duplications, inversions, deletions of entire regions—or the accidental exchange of whole parts of sequences between different chromosomes, chromosomal translocation.
This
is a diagram showing mutations in an RNA sequence. Figure (1) is a
normal RNA sequence, consisting of 4 codons. Figure (2) shows a
missense, single point, non silent mutation. Figures (3 and 4) both show
frameshift mutations,
which is why they are grouped together. Figure 3 shows a deletion of
the second base pair in the second codon. Figure 4 shows an insertion in
the third base pair of the second codon. Figure (5) shows a repeat
expansion, where an entire codon is duplicated.
Mutations alter an organism's genotype and occasionally this causes
different phenotypes to appear. Most mutations have little effect on an
organism's phenotype, health, or reproductive fitness. Mutations that do have an effect are usually detrimental, but occasionally some can be beneficial. Studies in the fly Drosophila melanogaster
suggest that if a mutation changes a protein produced by a gene, about
70 percent of these mutations are harmful with the remainder being
either neutral or weakly beneficial.
Over many generations, the genomes of organisms can change significantly, resulting in evolution. In the process called adaptation, selection for beneficial mutations can cause a species to evolve into forms better able to survive in their environment. New species are formed through the process of speciation, often caused by geographical separations that prevent populations from exchanging genes with each other.
By comparing the homology between different species' genomes, it is possible to calculate the evolutionary distance between them and when they may have diverged.
Genetic comparisons are generally considered a more accurate method of
characterizing the relatedness between species than the comparison of
phenotypic characteristics. The evolutionary distances between species
can be used to form evolutionary trees; these trees represent the common descent
and divergence of species over time, although they do not show the
transfer of genetic material between unrelated species (known as horizontal gene transfer and most common in bacteria).
Although geneticists originally studied inheritance in a wide variety
of organisms, the range of species studied has narrowed. One reason is
that when significant research already exists for a given organism, new
researchers are more likely to choose it for further study, and so
eventually a few model organisms became the basis for most genetics research. Common research topics in model organism genetics include the study of gene regulation and the involvement of genes in development and cancer. Organisms were chosen, in part, for convenience—short generation times and easy genetic manipulation made some organisms popular genetics research tools. Widely used model organisms include the gut bacterium Escherichia coli, the plant Arabidopsis thaliana, baker's yeast (Saccharomyces cerevisiae), the nematode Caenorhabditis elegans, the common fruit fly (Drosophila melanogaster), the zebrafish (Danio rerio), and the common house mouse (Mus musculus).
Medical genetics seeks to understand how genetic variation relates to human health and disease. When searching for an unknown gene that may be involved in a disease, researchers commonly use genetic linkage and genetic pedigree charts to find the location on the genome associated with the disease. At the population level, researchers take advantage of Mendelian randomization to look for locations in the genome that are associated with diseases, a method especially useful for multigenic traits not clearly defined by a single gene. Once a candidate gene is found, further research is often done on the corresponding (or homologous)
genes of model organisms. In addition to studying genetic diseases, the
increased availability of genotyping methods has led to the field of pharmacogenetics: the study of how genotype can affect drug responses.
Individuals differ in their inherited tendency to develop cancer,
and cancer is a genetic disease. The process of cancer development in
the body is a combination of events. Mutations occasionally occur within
cells in the body as they divide. Although these mutations will not be
inherited by any offspring, they can affect the behavior of cells,
sometimes causing them to grow and divide more frequently. There are
biological mechanisms that attempt to stop this process; signals are
given to inappropriately dividing cells that should trigger cell death, but sometimes additional mutations occur that cause cells to ignore these messages. An internal process of natural selection occurs within the body and eventually mutations accumulate within cells to promote their own growth, creating a cancerous tumor that grows and invades various tissues of the body. Normally, a cell divides only in response to signals called growth factors and stops growing once in contact with surrounding cells and in response to growth-inhibitory signals. It usually then divides a limited number of times and dies, staying within the epithelium
where it is unable to migrate to other organs. To become a cancer cell,
a cell has to accumulate mutations in a number of genes (three to
seven). A cancer cell can divide without growth factor and ignores
inhibitory signals. Also, it is immortal and can grow indefinitely, even
after it makes contact with neighboring cells. It may escape from the
epithelium and ultimately from the primary tumor.
Then, the escaped cell can cross the endothelium of a blood vessel and
get transported by the bloodstream to colonize a new organ, forming
deadly metastasis.
Although there are some genetic predispositions in a small fraction of
cancers, the major fraction is due to a set of new genetic mutations
that originally appear and accumulate in one or a small number of cells
that will divide to form the tumor and are not transmitted to the
progeny (somatic mutations). The most frequent mutations are a loss of function of p53 protein, a tumor suppressor, or in the p53 pathway, and gain of function mutations in the Ras proteins, or in other oncogenes.
DNA can be manipulated in the laboratory. Restriction enzymes are commonly used enzymes that cut DNA at specific sequences, producing predictable fragments of DNA. DNA fragments can be visualized through use of gel electrophoresis, which separates fragments according to their length.
The use of ligation enzymes
allows DNA fragments to be connected. By binding ("ligating") fragments
of DNA together from different sources, researchers can create recombinant DNA, the DNA often associated with genetically modified organisms. Recombinant DNA is commonly used in the context of plasmids: short circular DNA molecules with a few genes on them. In the process known as molecular cloning,
researchers can amplify the DNA fragments by inserting plasmids into
bacteria and then culturing them on plates of agar (to isolate clones of bacteria cells). "Cloning" can also refer to the various means of creating cloned ("clonal") organisms.
DNA can also be amplified using a procedure called the polymerase chain reaction (PCR).
By using specific short sequences of DNA, PCR can isolate and
exponentially amplify a targeted region of DNA. Because it can amplify
from extremely small amounts of DNA, PCR is also often used to detect
the presence of specific DNA sequences.
DNA sequencing, one of the most fundamental technologies developed to
study genetics, allows researchers to determine the sequence of
nucleotides in DNA fragments. The technique of chain-termination sequencing, developed in 1977 by a team led by Frederick Sanger,
is still routinely used to sequence DNA fragments. Using this
technology, researchers have been able to study the molecular sequences
associated with many human diseases.
As sequencing has become less expensive, researchers have sequenced the genomes of many organisms using a process called genome assembly, which uses computational tools to stitch together sequences from many different fragments. These technologies were used to sequence the human genome in the Human Genome Project completed in 2003. New high-throughput sequencing
technologies are dramatically lowering the cost of DNA sequencing, with
many researchers hoping to bring the cost of resequencing a human
genome down to a thousand dollars.
Next-generation sequencing
(or high-throughput sequencing) came about due to the ever-increasing
demand for low-cost sequencing. These sequencing technologies allow the
production of potentially millions of sequences concurrently. The large amount of sequence data available has created the subfield of genomics,
research that uses computational tools to search for and analyze
patterns in the full genomes of organisms. Genomics can also be
considered a subfield of bioinformatics, which uses computational approaches to analyze large sets of biological data. A common problem to these fields of research is how to manage and share data that deals with human subject and personally identifiable information.
On 19 March 2015, a group of leading biologists urged a worldwide ban on clinical use of methods, particularly the use of CRISPR and zinc finger, to edit the human genome in a way that can be inherited. In April 2015, Chinese researchers reported results of basic research to edit the DNA of non-viable human embryos using CRISPR.
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