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Heredity, also called inheritance or biological inheritance, is the passing on of
traits Trait may refer to: * Phenotypic trait in biology, which involve genes and characteristics of organisms * Trait (computer programming), a model for structuring object-oriented programs (a template class in the C++ programming language) * Trait the ...
from parents to their offspring; either through
asexual reproduction Asexual reproduction is a type of reproduction Reproduction (or procreation or breeding) is the biological process by which new individual organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organis ...
or
sexual reproduction Sexual reproduction is a type of reproduction that involves a complex Biological life cycle, life cycle in which a gamete (such as a sperm or egg cell) with a single set of chromosomes (haploid) combines with another to produce a zygote that devel ...
, the offspring
cells Cell most often refers to: * Cell (biology), the functional basic unit of life Cell may also refer to: Closed spaces * Monastic cell, a small room, hut, or cave in which a monk or religious recluse lives * Prison cell, a room used to hold peopl ...
or
organisms In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms are composed of cells (cell theory). Organisms are classified by taxonomy (biology), taxonomy into groups such as Multice ...

organisms
acquire the
genetic information A nucleic acid sequence is a succession of bases signified by a series of a set of five different letters that indicate the order of nucleotides Nucleotides are organic molecules consisting of a nucleoside and a phosphate. They serve as monom ...
of their parents. Through heredity, variations between individuals can accumulate and cause
species In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanis ...

species
to
evolve
evolve
by
natural selection Natural selection is the differential survival and reproduction of individuals due to differences in phenotype. It is a key mechanism of evolution, the change in the Heredity, heritable Phenotypic trait, traits characteristic of a populatio ...
. The study of heredity in
biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanisms, Developmenta ...

biology
is
genetics Genetics is a branch of biology concerned with the study of genes, genetic variation, and heredity in organisms.Hartl D, Jones E (2005) Though heredity had been observed for millennia, Gregor Mendel, Moravia, Moravian scientist and Augustinian ...

genetics
.


Overview

In humans,
eye color Eye color is a polygenicA polygene is a member of a group of non- epistatic gene In biology, a gene (from ''genos'' "...Wilhelm Johannsen coined the word gene to describe the Mendelian_inheritance#History, Mendelian units of heredity.. ...

eye color
is an example of an inherited characteristic: an individual might inherit the "brown-eye trait" from one of the parents. Inherited traits are controlled by
gene In biology, a gene (from ''genos'' "...Wilhelm Johannsen coined the word gene to describe the Mendelian_inheritance#History, Mendelian units of heredity..." (Greek language, Greek) meaning ''generation'' or ''birth'' ) is a basic unit of her ...

gene
s and the complete set of genes within an organism's
genome In the fields of molecular biology Molecular biology is the branch of biology that seeks to understand the molecule, molecular basis of biological activity in and between Cell (biology), cells, including biomolecule, molecular synthesis, ...

genome
is called its
genotype The genotype of an organism is its complete set of genetic material. Genotype can also be used to refer to the alleles An allele (, ; ; modern formation from Greek ἄλλος ''állos'', "other") is one of two, or more, forms of a given gene ...
. The complete set of observable traits of the structure and behavior of an organism is called its
phenotype right , Here the relation between genotype and phenotype is illustrated, using a Punnett square, for the character of petal color in pea plants. The letters B and b represent genes for color, and the pictures show the resultant phenotypes. Thi ...

phenotype
. These traits arise from the interaction of its genotype with the
environment Environment most often refers to: __NOTOC__ * Natural environment, all living and non-living things occurring naturally * Biophysical environment, the physical and biological factors along with their chemical interactions that affect an organism or ...
. As a result, many aspects of an organism's phenotype are not inherited. For example,
suntanned
suntanned
skin comes from the interaction between a person's genotype and sunlight; thus, suntans are not passed on to people's children. However, some people tan more easily than others, due to differences in their genotype: a striking example is people with the inherited trait of
albinism Albinism is the congenital absence of any pigmentation or colouration in a person, animal or plant, resulting in white hair, feathers, scales and skin and pink eyes in mammals, birds, reptiles, amphibians and fish and invertebrates as well. Va ...
, who do not tan at all and are very sensitive to
sunburn Sunburn is a form of radiation burn A radiation burn is a damage to the skin Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation. ...

sunburn
. Heritable traits are known to be passed from one generation to the next via
DNA Deoxyribonucleic acid (; DNA) is a molecule File:Pentacene on Ni(111) STM.jpg, A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five carbon rings. A molecule is an electrically neutral gro ...

DNA
, a
molecule File:Pentacene on Ni(111) STM.jpg, A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five carbon rings. A molecule is an electrically neutral group of two or more atoms held together by chemical bo ...

molecule
that encodes genetic information. DNA is a long
polymer A polymer (; Greek ''wikt:poly-, poly-'', "many" + ''wikt:-mer, -mer'', "part") is a Chemical substance, substance or material consisting of very large molecules, or macromolecules, composed of many Repeat unit, repeating subunits. Due to their ...

polymer
that incorporates four types of bases, which are interchangeable. The
Nucleic acid sequence A nucleic acid sequence is a succession of bases signified by a series of a set of five different letters that indicate the order of nucleotides Nucleotides are organic molecules consisting of a nucleoside and a phosphate. They serve as monom ...
(the sequence of bases along a particular DNA molecule) specifies the genetic information: this is comparable to a sequence of letters spelling out a passage of text. Before a cell divides through
mitosis In cell biology Cell biology (also cellular biology or cytology) is a branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical proces ...

mitosis
, the DNA is copied, so that each of the resulting two cells will inherit the DNA sequence. A portion of a DNA molecule that specifies a single functional unit is called a
gene In biology, a gene (from ''genos'' "...Wilhelm Johannsen coined the word gene to describe the Mendelian_inheritance#History, Mendelian units of heredity..." (Greek language, Greek) meaning ''generation'' or ''birth'' ) is a basic unit of her ...

gene
; different genes have different sequences of bases. Within
cells Cell most often refers to: * Cell (biology), the functional basic unit of life Cell may also refer to: Closed spaces * Monastic cell, a small room, hut, or cave in which a monk or religious recluse lives * Prison cell, a room used to hold peopl ...
, the long strands of DNA form condensed structures called
chromosome A chromosome is a long DNA The structure of part of a DNA double helix Deoxyribonucleic acid (; DNA) is a molecule File:Pentacene on Ni(111) STM.jpg, A scanning tunneling microscopy image of pentacene molecules, which consist of ...

chromosome
s. Organisms inherit genetic material from their parents in the form of
homologous chromosome A couple of homologous chromosomes, or homologs, are a set of one maternal and one paternal chromosome A chromosome is a long DNA The structure of part of a DNA double helix Deoxyribonucleic acid (; DNA) is a molecule File:Pen ...
s, containing a unique combination of DNA sequences that code for genes. The specific location of a DNA sequence within a chromosome is known as a
locus Locus (plural loci) is Latin for "place". It may refer to: Entertainment * Locus (comics), a Marvel Comics mutant villainess, a member of the Mutant Liberation Front * Locus (magazine), ''Locus'' (magazine), science fiction and fantasy magazine ...
. If the DNA sequence at a particular locus varies between individuals, the different forms of this sequence are called
allele An allele (, ; ; modern formation from Greek ἄλλος ''állos'', "other") is one of two, or more, forms of a given gene In biology, a gene (from ''genos'' "...Wilhelm Johannsen coined the word gene to describe the Mendelian_inheritance ...
s. DNA sequences can change through
mutation A red tulip exhibiting a partially yellow petal due to a mutation in its genes In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processe ...
s, producing new alleles. If a mutation occurs within a gene, the new allele may affect the trait that the gene controls, altering the phenotype of the organism. However, while this simple correspondence between an allele and a trait works in some cases, most traits are more complex and are controlled by multiple interacting genes within and among organisms. Developmental biologists suggest that complex interactions in genetic networks and communication among cells can lead to heritable variations that may underlie some of the mechanics in
developmental plasticityDevelopmental plasticity is a general term referring to changes in neural connections during development as a result of environmental interactions as well as neural changes induced by learning. Much like neuroplasticity or brain plasticity, developm ...
and canalization. Recent findings have confirmed important examples of heritable changes that cannot be explained by direct agency of the DNA molecule. These phenomena are classed as
epigenetic In biology, epigenetics is the study of heritability, heritable phenotype changes that do not involve alterations in the DNA sequence. The Ancient Greek, Greek prefix ''wikt:epi-, epi-'' ( "over, outside of, around") in ''epigenetics'' implies f ...
inheritance systems that are causally or independently evolving over genes. Research into modes and mechanisms of epigenetic inheritance is still in its scientific infancy, however, this area of research has attracted much recent activity as it broadens the scope of
heritability Heritability is a statistic used in the fields of Animal husbandry, breeding and genetics that estimates the degree of ''variation'' in a phenotypic trait in a population that is due to genetic variation between individuals in that population. It m ...

heritability
and evolutionary biology in general.
DNA methylation DNA methylation is a biological process by which methyl group A methyl group is an alkyl In organic chemistry, an alkyl substituent A substituent is one or a group of atom An atom is the smallest unit of ordinary matter In cl ...

DNA methylation
marking
chromatin Chromatin is a complex of DNA, protein Proteins are large biomolecules or macromolecules that are comprised of one or more long chains of amino acid residue (biochemistry), residues. Proteins perform a vast array of functions within organisms ...
, self-sustaining , gene silencing by
RNA interference RNA interference (RNAi) is a biological process in which RNA molecules are involved in sequence-specific suppression of gene expression by double-stranded RNA, through translation or transcriptional repression. Historically, RNAi was known by othe ...
, and the three dimensional
conformation Conformation generally means structural arrangement and may refer to: * Conformational isomerism, a form of stereoisomerism in chemistry ** Carbohydrate conformation ** Cyclohexane conformation ** Protein conformation ** Conformation activity relat ...

conformation
of proteins (such as
prions Prions are Protein folding, misfolded proteins with the ability to transmit their misfolded shape onto normal variants of the same protein. They characterize several fatal and transmissible neurodegenerative diseases in humans and many other ani ...
) are areas where epigenetic inheritance systems have been discovered at the organismic level. Heritability may also occur at even larger scales. For example, ecological inheritance through the process of
niche construction Niche construction is the process by which an organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual contiguous system that embodies the Life#Biology, properties of life. It is ...
is defined by the regular and repeated activities of organisms in their environment. This generates a legacy of effect that modifies and feeds back into the selection regime of subsequent generations. Descendants inherit genes plus environmental characteristics generated by the ecological actions of ancestors. Other examples of heritability in evolution that are not under the direct control of genes include the inheritance of cultural traits, group heritability, and
symbiogenesis Symbiogenesis, endosymbiotic theory, or serial endosymbiotic theory is the leading evolutionary theory of the origin of eukaryotic cells from prokaryotic organisms. The theory holds that mitochondria, plastids such as chloroplasts, and possibly oth ...

symbiogenesis
. These examples of heritability that operate above the gene are covered broadly under the title of multilevel or hierarchical selection, which has been a subject of intense debate in the history of evolutionary science.


Relation to theory of evolution

When
Charles Darwin Charles Robert Darwin (; ; 12 February 1809 – 19 April 1882) was an English natural history#Before 1900, naturalist, geologist and biologist, best known for his contributions to the science of evolution. His proposition that all spe ...

Charles Darwin
proposed his theory of
evolution Evolution is change in the heritable Heredity, also called inheritance or biological inheritance, is the passing on of Phenotypic trait, traits from parents to their offspring; either through asexual reproduction or sexual reproduction, ...

evolution
in 1859, one of its major problems was the lack of an underlying mechanism for heredity. Darwin believed in a mix of blending inheritance and the inheritance of acquired
traits Trait may refer to: * Phenotypic trait in biology, which involve genes and characteristics of organisms * Trait (computer programming), a model for structuring object-oriented programs (a template class in the C++ programming language) * Trait the ...
(
pangenesis Pangenesis was Charles Darwin's hypothetical mechanism for heredity, in which he proposed that each part of the body continually emitted its own type of small organic particles called gemmules that aggregated in the gonads, contributing heritable ...

pangenesis
). Blending inheritance would lead to uniformity across populations in only a few generations and then would remove variation from a population on which natural selection could act. This led to Darwin adopting some Lamarckian ideas in later editions of ''
On the Origin of Species ''On the Origin of Species'' (or, more completely, ''On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life''),The book's full original title was ''On the Origin of Species by Mea ...
'' and his later biological works. Darwin's primary approach to heredity was to outline how it appeared to work (noticing that traits that were not expressed explicitly in the parent at the time of reproduction could be inherited, that certain traits could be
sex-linked Sex linked describes the sex-specific patterns of inheritance Inheritance is the practice of passing on private property, Title (property), titles, debts, entitlements, Privilege (law), privileges, rights, and Law of obligations, obligations ...
, etc.) rather than suggesting mechanisms. Darwin's initial model of heredity was adopted by, and then heavily modified by, his cousin
Francis Galton Sir Francis Galton, FRS (; 16 February 1822 – 17 January 1911), was an English Victorian era In the history of the United Kingdom, the Victorian era was the wikt:period, period of Queen Victoria's reign, from 20 June 1837 unti ...

Francis Galton
, who laid the framework for the
biometric Biometrics are body measurements and calculations related to human characteristics. Biometrics authentication Authentication (from ''authentikos'', "real, genuine", from αὐθέντης ''authentes'', "author") is the act of proof (truth) ...

biometric
school of heredity. Galton found no evidence to support the aspects of Darwin's pangenesis model, which relied on acquired traits. The inheritance of acquired traits was shown to have little basis in the 1880s when
August Weismann Prof August Friedrich Leopold Weismann FRS (For), HonFRSE, LLD (17 January 18345 November 1914) was a German evolutionary biologist. Ernst Mayr Ernst Walter Mayr (; 5 July 1904 – 3 February 2005) was one of the 20th century's leading ...

August Weismann
cut the
tail The tail is the section at the rear end of certain kinds of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotrop ...
s off many generations of
mice A mouse, plural mice, is a small mammal Mammals (from Latin language, Latin , 'breast') are a group of vertebrate animals constituting the class (biology), class Mammalia (), and characterized by the presence of mammary glands which i ...

mice
and found that their offspring continued to develop tails.


History

Scientists in
Antiquity Antiquity or Antiquities may refer to Historical objects or periods Artifacts * Antiquities, objects or artifacts surviving from ancient cultures Eras Any period before the European Middle Ages In the history of Europe, the Middle Ages ...
had a variety of ideas about heredity:
Theophrastus Theophrastus (; grc-gre, Θεόφραστος ; c. 371c. 287 BC), a Greek native of Eresos Eresos (; el, Ερεσός; grc, Ἔρεσος) and its twin beach village Skala Eresou are located in the southwest part of the Greek island of Le ...

Theophrastus
proposed that male flowers caused female flowers to ripen;
Hippocrates Hippocrates of Kos (; grc-gre, Ἱπποκράτης ὁ Κῷος, Hippokrátēs ho Kôios; ), also known as Hippocrates II, was a Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), ...

Hippocrates
speculated that "seeds" were produced by various body parts and transmitted to offspring at the time of conception; and
Aristotle Aristotle (; grc-gre, Ἀριστοτέλης ''Aristotélēs'', ; 384–322 BC) was a Greek philosopher A philosopher is someone who practices philosophy. The term ''philosopher'' comes from the grc, φιλόσοφος, , translit ...

Aristotle
thought that male and female fluids mixed at conception.
Aeschylus Aeschylus (, ; grc-gre, Αἰσχύλος ; c. 525/524 – c. 456/455 BC) was an ancient Greece, ancient Greek Greek tragedy, tragedian, and is often described as the father of tragedy. Academic knowledge of the genre begins with his work, and ...
, in 458 BC, proposed the male as the parent, with the female as a "nurse for the young life sown within her". Ancient understandings of heredity transitioned to two debated doctrines in the 18th century. The Doctrine of Epigenesis and the Doctrine of Preformation were two distinct views of the understanding of heredity. The Doctrine of Epigenesis, originated by
Aristotle Aristotle (; grc-gre, Ἀριστοτέλης ''Aristotélēs'', ; 384–322 BC) was a Greek philosopher A philosopher is someone who practices philosophy. The term ''philosopher'' comes from the grc, φιλόσοφος, , translit ...

Aristotle
, claimed that an embryo continually develops. The modifications of the parent's traits are passed off to an embryo during its lifetime. The foundation of this doctrine was based on the theory of inheritance of acquired traits. In direct opposition, the Doctrine of Preformation claimed that "like generates like" where the germ would evolve to yield offspring similar to the parents. The Preformationist view believed procreation was an act of revealing what had been created long before. However, this was disputed by the creation of the
cell theory In biology, cell theory is a scientific theory first formulated in the mid-nineteenth century, that living organisms are made up of Cell (biology), cells, that they are the basic structural/organizational unit of all organisms, and that all cells ...
in the 19th century, where the fundamental unit of life is the cell, and not some preformed parts of an organism. Various hereditary mechanisms, including
blending inheritance Blending inheritance is an Superseded scientific theories, obsolete theory in biology from the 19th century. The theory is that the progeny inheritance (biology), inherits any characteristic as the average of the parents' values of that characteris ...

blending inheritance
were also envisaged without being properly tested or quantified, and were later disputed. Nevertheless, people were able to develop domestic breeds of animals as well as crops through artificial selection. The inheritance of acquired traits also formed a part of early Lamarckian ideas on evolution. During the 18th century, Dutch microscopist
Antonie van Leeuwenhoek Antonie Philips van Leeuwenhoek ( ; ; 24 October 1632 – 26 August 1723) was a Dutch Republic, Dutch businessman and scientist in the Dutch Golden Age, Golden Age of Dutch science and technology. A largely self-taught man in science, he is ...
(1632–1723) discovered "animalcules" in the sperm of humans and other animals. Some scientists speculated they saw a "little man" (
homunculus A homunculus ( , , ; "little person") is a representation of a small human being. Popularized in sixteenth-century alchemy File:Aurora consurgens zurich 044 f-21v-44 dragon-pot.jpg, Depiction of Ouroboros from the alchemical treatise ''Aurora ...
) inside each
sperm Sperm is the male Male (♂) is the sex of an organism that produces the gamete known as sperm. A male gamete can fuse with a larger female gamete, or ovum, in the process of fertilization. A male cannot sexual reproduction, reproduce sexuall ...
. These scientists formed a school of thought known as the "spermists". They contended the only contributions of the female to the next generation were the womb in which the homunculus grew, and prenatal influences of the womb. An opposing school of thought, the ovists, believed that the future human was in the egg, and that sperm merely stimulated the growth of the egg. Ovists thought women carried eggs containing boy and girl children, and that the gender of the offspring was determined well before conception. An early research initiative emerged in 1878 when
Alpheus Hyatt Alpheus Hyatt (April 5, 1838 – January 15, 1902) was an American zoologist and paleontology, palaeontologist. Biography Alpheus Hyatt II was born in Washington, D.C. to Alpheus Hyatt and Harriet Randolph (King) Hyatt. He briefly attended ...

Alpheus Hyatt
led an investigation to study the laws of heredity through compiling data on family phenotypes (nose size, ear shape, etc.) and expression of pathological conditions and abnormal characteristics, particularly with respect to the age of appearance. One of the projects aims was to tabulate data to better understand why certain traits are consistently expressed while others are highly irregular.


Gregor Mendel: father of genetics

The idea of particulate inheritance of genes can be attributed to the
Moravia Moravia ( , also , ; cs, Morava ; german: link=no, Mähren ; pl, Morawy ; szl, Morawa; la, Moravia) is a historical region in the east of the Czech Republic and one of three historical Czech lands, with Bohemia and Czech Silesia. The medi ...

Moravia
n monk
Gregor Mendel Gregor Johann Mendel (; cs, Řehoř Jan Mendel; 20 July 1822 – 6 January 1884) was a meteorologist, mathematician, biologist, AugustinianAugustinian may refer to: *Augustinians Augustinians are members of Christian religious orders tha ...

Gregor Mendel
who published his work on pea plants in 1865. However, his work was not widely known and was rediscovered in 1901. It was initially assumed that
Mendelian inheritance Mendelian inheritance is a type of biological Biology is the natural science Natural science is a branch of science Science (from the Latin word ''scientia'', meaning "knowledge") is a systematic enterprise that Scientific me ...

Mendelian inheritance
only accounted for large (qualitative) differences, such as those seen by Mendel in his pea plants – and the idea of additive effect of (quantitative) genes was not realised until R.A. Fisher's (1918) paper, "
The Correlation Between Relatives on the Supposition of Mendelian Inheritance "The Correlation between Relatives on the Supposition of Mendelian Inheritance" is a science, scientific paper by Ronald Fisher which was published in the ''Transactions of the Royal Society of Edinburgh'' in 1918, (volume 52, pages 399–433). ...
" Mendel's overall contribution gave scientists a useful overview that traits were inheritable. His pea plant demonstration became the foundation of the study of Mendelian Traits. These traits can be traced on a single locus.Carlson, Neil R. (2010). ''Psychology: the Science of Behavior'', p. 206. Toronto: Pearson Canada. .


Modern development of genetics and heredity

In the 1930s, work by Fisher and others resulted in a combination of Mendelian and biometric schools into the modern evolutionary synthesis. The modern synthesis bridged the gap between experimental geneticists and naturalists; and between both and palaeontologists, stating that: # All evolutionary phenomena can be explained in a way consistent with known genetic mechanisms and the observational evidence of naturalists. # Evolution is gradual: small genetic changes, recombination ordered by
natural selection Natural selection is the differential survival and reproduction of individuals due to differences in phenotype. It is a key mechanism of evolution, the change in the Heredity, heritable Phenotypic trait, traits characteristic of a populatio ...
. Discontinuities amongst species (or other taxa) are explained as originating gradually through geographical separation and extinction (not saltation). #
Selection Selection may refer to: In science: * Selection (biology) Natural selection is the differential survival and reproduction of individuals due to differences in phenotype right , Here the relation between genotype and phenotype is ill ...
is overwhelmingly the main mechanism of change; even slight advantages are important when continued. The object of selection is the
phenotype right , Here the relation between genotype and phenotype is illustrated, using a Punnett square, for the character of petal color in pea plants. The letters B and b represent genes for color, and the pictures show the resultant phenotypes. Thi ...

phenotype
in its surrounding environment. The role of
genetic drift Genetic drift (allelic drift or the Sewall Wright effect) is the change in the frequency of an existing gene In biology, a gene (from ''genos'' "...Wilhelm Johannsen coined the word gene to describe the Mendelian_inheritance#History, Me ...

genetic drift
is equivocal; though strongly supported initially by Dobzhansky, it was downgraded later as results from ecological genetics were obtained. # The primacy of population thinking: the genetic diversity carried in natural populations is a key factor in evolution. The strength of natural selection in the wild was greater than expected; the effect of ecological factors such as niche occupation and the significance of barriers to gene flow are all important. The idea that
speciation Speciation is the evolution Evolution is change in the Heredity, heritable Phenotypic trait, characteristics of biological populations over successive generations. These characteristics are the Gene expression, expressions of genes that are ...

speciation
occurs after populations are reproductively isolated has been much debated. In plants, polyploidy must be included in any view of speciation. Formulations such as 'evolution consists primarily of changes in the frequencies of alleles between one generation and another' were proposed rather later. The traditional view is that developmental biology ('
evo-devo Evolutionary developmental biology (informally, evo-devo) is a field of biological research that compares the developmental biology, developmental processes of different organisms to inference, infer the phylogeny, ancestral relationships between ...
') played little part in the synthesis, but an account of
Gavin de Beer Sir Gavin Rylands de Beer (1 November 1899 – 21 June 1972) was a British evolution Evolution is change in the Heredity, heritable Phenotypic trait, characteristics of biological populations over successive generations. These characteristi ...
's work by
Stephen Jay Gould Stephen Jay Gould (; September 10, 1941 – May 20, 2002) was an American Paleontology, paleontologist, Evolutionary biology, evolutionary biologist, and History of science, historian of science. He was one of the most influential and widely read ...
suggests he may be an exception. Almost all aspects of the synthesis have been challenged at times, with varying degrees of success. There is no doubt, however, that the synthesis was a great landmark in evolutionary biology. It cleared up many confusions, and was directly responsible for stimulating a great deal of research in the post-
World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a World war, global war that lasted from 1939 to 1945. It involved World War II by country, the vast majority of the world's countries—including all the great ...
era.
Trofim Lysenko Trofím Denísovich Lysénko (russian: Трофи́м Дени́сович Лысе́нко, uk, Трохи́м Дени́сович Лисе́нко, Trokhym Denysovych Lysenko; 20 November 1976) was a Soviet agronomist and biologist France ...
however caused a backlash of what is now called
Lysenkoism Lysenkoism ( rus , Лысе́нковщина , Lysenkovshchina) was a political campaign led by Trofim Lysenko against genetics Genetics is a branch of biology concerned with the study of genes, genetic variation, and heredity in organisms ...
in the
Soviet Union The Soviet Union,. officially the Union of Soviet Socialist Republics. (USSR),. was a Federalism, federal socialist state in Northern Eurasia that existed from 1922 to 1991. Nominally a Political union, union of multiple national Republics of t ...
when he emphasised Lamarckian ideas on the inheritance of acquired traits. This movement affected agricultural research and led to food shortages in the 1960s and seriously affected the USSR. There is growing evidence that there is transgenerational inheritance of epigenetic changes in humans and other animals.


Common genetic disorders

:*
Fragile X syndrome Fragile X syndrome (FXS) is a genetic disorder A genetic disorder is a health problem caused by one or more abnormalities in the genome. It can be caused by a mutation in a single gene In biology, a gene (from ''genos'' "...Wilhelm Jo ...
:*
Sickle cell disease Sickle cell disease (SCD) is a group of blood disorders typically inherited from a person's parents. The most common type is known as sickle cell anaemia (SCA). It results in an abnormality in the oxygen-carrying protein haemoglobin found in ...
:*
Phenylketonuria Phenylketonuria (PKU) is an inborn error of metabolism Inborn errors of metabolism form a large class of genetic disease A genetic disorder is a health problem caused by one or more abnormalities in the genome. It can be caused by a mutati ...
(PKU) :*
Haemophilia Haemophilia or hemophilia (from Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its popu ...


Types

The description of a mode of biological inheritance consists of three main categories: :1. Number of involved
loci Locus (plural loci) is Latin for "place". It may refer to: Entertainment * Locus (comics), a Marvel Comics mutant villainess, a member of the Mutant Liberation Front * Locus (magazine), ''Locus'' (magazine), science fiction and fantasy magazine ...
:* (also called "simple") – one
locus Locus (plural loci) is Latin for "place". It may refer to: Entertainment * Locus (comics), a Marvel Comics mutant villainess, a member of the Mutant Liberation Front * Locus (magazine), ''Locus'' (magazine), science fiction and fantasy magazine ...
:* Oligogenic – few loci :*
PolygeneA polygene is a member of a group of non- epistatic gene In biology, a gene (from ''genos'' "...Wilhelm Johannsen coined the word gene to describe the Mendelian_inheritance#History, Mendelian units of heredity..." (Greek language, Greek) mean ...
tic – many loci :2. Involved
chromosome A chromosome is a long DNA The structure of part of a DNA double helix Deoxyribonucleic acid (; DNA) is a molecule File:Pentacene on Ni(111) STM.jpg, A scanning tunneling microscopy image of pentacene molecules, which consist of ...

chromosome
s :*
Autosomal An autosome is any chromosome that is not a sex chromosome (an allosome). The members of an autosome pair in a diploid Ploidy () is the number of complete sets of chromosome A chromosome is a long DNA molecule with part or all of the ...
– loci are not situated on a
sex chromosome A sex chromosome (also referred to as an allosome, heterotypical chromosome, gonosome, heterochromosome, or idiochromosome) is a chromosome that differs from an ordinary autosome in form, size, and behavior. The human sex chromosomes, a typical p ...
:* Gonosomal – loci are situated on a
sex chromosome A sex chromosome (also referred to as an allosome, heterotypical chromosome, gonosome, heterochromosome, or idiochromosome) is a chromosome that differs from an ordinary autosome in form, size, and behavior. The human sex chromosomes, a typical p ...
:**X-chromosomal – loci are situated on the
X-chromosome The X chromosome is one of the two sex-determining chromosomes (allosomes) in many organisms, including mammals (the other is the Y chromosome), and is found in both males and females. It is a part of the XY sex-determination system and X0 sex-det ...

X-chromosome
(the more common case) :**Y-chromosomal – loci are situated on the
Y-chromosome The Y chromosome is one of two sex chromosome A chromosome is a long DNA molecule with part or all of the genetic material of an organism. Most eukaryotic chromosomes include packaging proteins called histones which, aided by chaperone p ...
:*
Mitochondrial A mitochondrion (, plural mitochondria) is a double membrane-bound organelle In cell biology, an organelle is a specialized subunit, usually within a cell (biology), cell, that has a specific function. The name ''organelle'' comes from the ide ...

Mitochondrial
– loci are situated on the
mitochondrial DNA File:Electron microscopy reveals mitochondrial DNA in discrete foci.jpg, Electron microscopy reveals mitochondrial DNA in discrete foci. Bars: 200 nm. (A) Cytoplasmic section after immunogold labelling with anti-DNA; gold particles marking mtD ...

mitochondrial DNA
:3. Correlation
genotype The genotype of an organism is its complete set of genetic material. Genotype can also be used to refer to the alleles An allele (, ; ; modern formation from Greek ἄλλος ''állos'', "other") is one of two, or more, forms of a given gene ...
phenotype right , Here the relation between genotype and phenotype is illustrated, using a Punnett square, for the character of petal color in pea plants. The letters B and b represent genes for color, and the pictures show the resultant phenotypes. Thi ...

phenotype
:*
Dominant Domination or dominant may refer to: Society * World domination, which is mainly a conspiracy theory * Colonialism in which one group (usually a nation) invades another region for material gain or to eliminate competition * Chauvinism in which a p ...
:*Intermediate (also called " codominant") :*
Recessive In genetics Genetics is a branch of biology concerned with the study of genes, genetic variation, and heredity in organisms.Hartl D, Jones E (2005) Though heredity had been observed for millennia, Gregor Mendel, Moravia, Moravian scientis ...
:* Overdominant :* Underdominant These three categories are part of every exact description of a mode of inheritance in the above order. In addition, more specifications may be added as follows: :4. Coincidental and environmental interactions :*
PenetrancePenetrance in genetics Genetics is a branch of biology concerned with the study of genes, genetic variation, and heredity in organisms.Hartl D, Jones E (2005) Though heredity had been observed for millennia, Gregor Mendel, Moravia, Moravian sc ...
:**Complete :**Incomplete (percentual number) :* Expressivity :**Invariable :**Variable :*
Heritability Heritability is a statistic used in the fields of Animal husbandry, breeding and genetics that estimates the degree of ''variation'' in a phenotypic trait in a population that is due to genetic variation between individuals in that population. It m ...

Heritability
(in polygenetic and sometimes also in oligogenetic modes of inheritance) :*Maternal or paternal imprinting phenomena (also see
epigenetics In biology, epigenetics is the study of heritability, heritable phenotype changes that do not involve alterations in the DNA sequence. The Ancient Greek, Greek prefix ''wikt:epi-, epi-'' ( "over, outside of, around") in ''epigenetics'' implies f ...
) :5. Sex-linked interactions :*Sex-linked inheritance ( gonosomal loci) :* Sex-limited phenotype expression (e.g., cryptorchism) :*Inheritance through the maternal line (in case of
mitochondrial DNA File:Electron microscopy reveals mitochondrial DNA in discrete foci.jpg, Electron microscopy reveals mitochondrial DNA in discrete foci. Bars: 200 nm. (A) Cytoplasmic section after immunogold labelling with anti-DNA; gold particles marking mtD ...

mitochondrial DNA
loci) :*Inheritance through the paternal line (in case of Y-chromosomal loci) :6. Locus–locus interactions :*
Epistasis File:Epistasis.png, Example of epistasis in coat colour genetics: If no pigments can be produced the other coat colour genes have no effect on the phenotype, no matter if they are dominant or if the individual is homozygous. Here the genotype "c ...

Epistasis
with other loci (e.g.,
overdominance Overdominance is a condition in genetics where the phenotype right , Here the relation between genotype and phenotype is illustrated, using a Punnett square, for the character of petal color in pea plants. The letters B and b represent genes f ...
) :*
Gene coupling In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechani ...
with other loci (also see crossing over) :*Homozygotous lethal factors :* Semi-lethal factors Determination and description of a mode of inheritance is also achieved primarily through statistical analysis of pedigree data. In case the involved loci are known, methods of
molecular genetics Molecular genetics is a sub-field of biology that addresses how differences in the structures or expression of DNA molecules manifests as variation among organisms. Molecular genetics often applies an "investigative approach" to determine the ...
can also be employed.


Dominant and recessive alleles

An
allele An allele (, ; ; modern formation from Greek ἄλλος ''állos'', "other") is one of two, or more, forms of a given gene In biology, a gene (from ''genos'' "...Wilhelm Johannsen coined the word gene to describe the Mendelian_inheritance ...
is said to be dominant if it is always expressed in the appearance of an organism (phenotype) provided that at least one copy of it is present. For example, in peas the allele for green pods, ''G'', is dominant to that for yellow pods, ''g''. Thus pea plants with the pair of alleles ''either'' ''GG'' (homozygote) ''or'' ''Gg'' (heterozygote) will have green pods. The allele for yellow pods is recessive. The effects of this allele are only seen when it is present in both chromosomes, ''gg'' (homozygote). This derives from Zygosity, the degree to which both copies of a chromosome or gene have the same genetic sequence, in other words, the degree of similarity of the alleles in an organism.


See also


References


External links


Stanford Encyclopedia of Philosophy entry on Heredity and Heritability

""Experiments in Plant Hybridization" (1866), by Johann Gregor Mendel," by A. Andrei at the Embryo Project Encyclopedia
{{Authority control Genetics