Heredity

Heredity is the passing on of traits from parents to their offspring, either through asexual reproduction or sexual reproduction, the offspring cells or organisms acquire the genetic information of their parents. Through heredity, variations between individuals can accumulate and cause species to evolve by natural selection. The study of heredity in biology is genetics.

Overview

Jug Ear Heredity
Heredity of phenotypic traits: Father and son with prominent ears and crowns.
ADN animation
DNA structure. Bases are in the centre, surrounded by phosphate–sugar chains in a double helix.

In humans, eye color is an example of an inherited characteristic: an individual might inherit the "brown-eye trait" from one of the parents.[1] Inherited traits are controlled by genes and the complete set of genes within an organism's genome is called its genotype.[2]

The complete set of observable traits of the structure and behavior of an organism is called its phenotype. These traits arise from the interaction of its genotype with the environment.[3] As a result, many aspects of an organism's phenotype are not inherited. For example, suntanned skin comes from the interaction between a person's phenotype and sunlight;[4] thus, suntans are not passed on to people's children. However, some people tan more easily than others, due to differences in their genotype:[5] a striking example is people with the inherited trait of albinism, who do not tan at all and are very sensitive to sunburn.[6]

Heritable traits are known to be passed from one generation to the next via DNA, a molecule that encodes genetic information.[2] DNA is a long polymer that incorporates four types of bases, which are interchangeable. 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.[7] Before a cell divides through 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; different genes have different sequences of bases. Within cells, the long strands of DNA form condensed structures called chromosomes. Organisms inherit genetic material from their parents in the form of homologous chromosomes, 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. If the DNA sequence at a particular locus varies between individuals, the different forms of this sequence are called alleles. DNA sequences can change through mutations, 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.[8]

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.[9][10] 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 plasticity and canalization.[11]

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 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 and evolutionary biology in general.[12] DNA methylation marking chromatin, self-sustaining metabolic loops, gene silencing by RNA interference, and the three dimensional conformation of proteins (such as prions) are areas where epigenetic inheritance systems have been discovered at the organismic level.[13][14] Heritability may also occur at even larger scales. For example, ecological inheritance through the process of niche construction 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.[15] 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.[16][17][18] 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.[17][19]

Relation to theory of evolution

When Charles Darwin proposed his theory of evolution in 1859, one of its major problems was the lack of an underlying mechanism for heredity.[20] Darwin believed in a mix of blending inheritance and the inheritance of acquired traits (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.[21] This led to Darwin adopting some Lamarckian ideas in later editions of On the Origin of Species and his later biological works.[22] 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, etc.) rather than suggesting mechanisms.

Darwin's initial model of heredity was adopted by, and then heavily modified by, his cousin Francis Galton, who laid the framework for the biometric school of heredity.[23] Galton found no evidence to support the aspects of Darwin's pangenesis model, which relied on acquired traits.[24]

The inheritance of acquired traits was shown to have little basis in the 1880s when August Weismann cut the tails off many generations of mice and found that their offspring continued to develop tails.[25]

History

Aristotle's model of Inheritance
Aristotle's model of inheritance. The heat/cold part is largely symmetrical, though influenced on the father's side by other factors; but the form part is not.

Scientists in Antiquity had a variety of ideas about heredity: Theophrastus proposed that male flowers caused female flowers to ripen;[26] Hippocrates speculated that "seeds" were produced by various body parts and transmitted to offspring at the time of conception;[27] and Aristotle thought that male and female fluids mixed at conception.[28] Aeschylus, in 458 BC, proposed the male as the parent, with the female as a "nurse for the young life sown within her".[29]

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, 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 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 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 (1632–1723) discovered "animalcules" in the sperm of humans and other animals.[30] Some scientists speculated they saw a "little man" (homunculus) inside each sperm. 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.[31] 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.[32]

Gregor Mendel: father of genetics

Independent assortment & segregation
Table showing how the genes exchange according to segregation or independent assortment during meiosis and how this translates into Mendel's laws

The idea of particulate inheritance of genes can be attributed to the Moravian[33] monk 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 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" 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.[34]

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:[35][36]

  1. All evolutionary phenomena can be explained in a way consistent with known genetic mechanisms and the observational evidence of naturalists.
  2. Evolution is gradual: small genetic changes, recombination ordered by natural selection. Discontinuities amongst species (or other taxa) are explained as originating gradually through geographical separation and extinction (not saltation).
  3. Selection is overwhelmingly the main mechanism of change; even slight advantages are important when continued. The object of selection is the phenotype in its surrounding environment. The role of genetic drift is equivocal; though strongly supported initially by Dobzhansky, it was downgraded later as results from ecological genetics were obtained.
  4. 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 occurs after populations are reproductively isolated has been much debated.[37] 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') played little part in the synthesis, but an account of Gavin de Beer's work by Stephen Jay Gould suggests he may be an exception.[38]

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.[39] It cleared up many confusions, and was directly responsible for stimulating a great deal of research in the post-World War II era.

Trofim Lysenko however caused a backlash of what is now called Lysenkoism in the Soviet Union 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.[40]

There is growing evidence that there is transgenerational inheritance of epigenetic changes in humans[41] and other animals.[42]

Common genetic disorders

Types

Autosomal dominant
An example pedigree chart of an autosomal dominant disorder.
Autosomal recessive
An example pedigree chart of an autosomal recessive disorder.
Sex linked inheritance
An example pedigree chart of a sex-linked disorder (the gene is on the X chromosome)

Dominant and recessive alleles

An allele 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).

The description of a mode of biological inheritance consists of three main categories:

1. Number of involved loci
  • Monogenetic (also called "simple") – one locus
  • Oligogenetic – few loci
  • Polygenetic – many loci
2. Involved chromosomes
3. Correlation genotypephenotype

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
5. Sex-linked interactions
6. Locus–locus interactions

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 can also be employed.

See also

References

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External links

Boveri–Sutton chromosome theory

The Boveri–Sutton chromosome theory (also known as the chromosome theory of inheritance or the Sutton–Boveri theory) is a fundamental unifying theory of genetics which identifies chromosomes as the carriers of genetic material. It correctly explains the mechanism underlying the laws of Mendelian inheritance by identifying chromosomes with the paired factors (particles) required by Mendel's laws. It also states that chromosomes are linear structures with genes located at specific sites called loci along them.It states simply that chromosomes, which are seen in all dividing cells and pass from one generation to the next, are the basis for all genetic inheritance.

Over a period of time random mutation

creates changes in the DNA sequence of a gene. Genes are located on chromosomes.

Genetic

Genetic may refer to:

Genetics, in biology, the science of genes, heredity, and the variation of organisms

Genetic, used as an adjective, refers to genes

Genetic disorder, any disorder caused by a genetic mutation, whether inherited or de novo

Genetic mutation, a change in a gene

Heredity, genes and their mutations being passed from parents to offspring

Genetic recombination, refers to the recombining of alleles resulting in a new molecule of DNA

Genetic (linguistics), in linguistics, a relationship between two languages with a common ancestor language

Genetic algorithm, in computer science, a kind of search technique modeled on evolutionary biology

Geneticist

A geneticist is a biologist who studies genetics, the science of genes, heredity, and variation of organisms.

Gregor Mendel

Gregor Johann Mendel (Czech: Řehoř Jan Mendel; 20 July 1822 – 6 January 1884) (English: ) was a scientist, Augustinian friar and abbot of St. Thomas' Abbey in Brno, Margraviate of Moravia. Mendel was born in a German-speaking family in the Silesian part of the Austrian Empire (today's Czech Republic) and gained posthumous recognition as the founder of the modern science of genetics. Though farmers had known for millennia that crossbreeding of animals and plants could favor certain desirable traits, Mendel's pea plant experiments conducted between 1856 and 1863 established many of the rules of heredity, now referred to as the laws of Mendelian inheritance.Mendel worked with seven characteristics of pea plants: plant height, pod shape and color, seed shape and color, and flower position and color. Taking seed color as an example, Mendel showed that when a true-breeding yellow pea and a true-breeding green pea were cross-bred their offspring always produced yellow seeds. However, in the next generation, the green peas reappeared at a ratio of 1 green to 3 yellow. To explain this phenomenon, Mendel coined the terms “recessive” and “dominant” in reference to certain traits. (In the preceding example, the green trait, which seems to have vanished in the first filial generation, is recessive and the yellow is dominant.) He published his work in 1866, demonstrating the actions of invisible “factors”—now called genes—in predictably determining the traits of an organism.

The profound significance of Mendel's work was not recognized until the turn of the 20th century (more than three decades later) with the rediscovery of his laws. Erich von Tschermak, Hugo de Vries, Carl Correns and William Jasper Spillman independently verified several of Mendel's experimental findings, ushering in the modern age of genetics.

Hereditary gingival fibromatosis

Hereditary gingival fibromatosis (HGF), also known as idiopathic gingival hyperplasia, is a rare condition of gingival overgrowth. HGF is characterized as a benign, slowly progressive, nonhemorrhagic, fibrous enlargement of keratinized gingiva. It can cover teeth in various degrees, and can lead to aesthetic disfigurement. Fibrous enlargement is most common in areas of maxillary and mandibular tissues of both arches in the mouth. Phenotype and genotype frequency of HGF is 1:175,000 where males and females are equally affected but the cause is not entirely known. It mainly exists as an isolated abnormality but can also be associated with a multi-system syndrome.

Heredity (journal)

Heredity is a scientific journal concerned with heredity in a biological sense, i.e. genetics. It was founded by Ronald Fisher and C. D. Darlington in 1947 and is the official journal of The Genetics Society. From 1996 the publishing was taken over by Nature Publishing Group.

Heredity (short story)

"Heredity" is a science fiction short story by the American writer Isaac Asimov. Asimov wrote the story, his twenty-third, in August 1940 under the title "Twins". It was rejected by John W. Campbell, editor of Astounding Science Fiction, on 29 August, and accepted by Frederik Pohl on 4 September. It appeared in the April 1941 issue of Astonishing Stories under the title "Heredity" and was reprinted in the 1972 collection The Early Asimov. Heredity was the second Asimov story to receive a cover illustration.

Heredity in Relation to Eugenics

Heredity in Relation to Eugenics is a book by American eugenicist Charles Benedict Davenport, published in 1911. It argued that many human traits were genetically inherited, and that it would therefore be possible to selectively breed people for desirable traits to improve the human race. It was printed and published with money and support of the Carnegie Institution. The book was widely used as a text for medical schools in the United States and abroad.In its time, the book was a success and became one of the most influential books in the early-20th century eugenics movement in the United States. By the 1940's, however, the science in the book had become to generally be regarded as seriously flawed, and the book was blamed by some for contributing to widespread eugenic sterilization programs in the United States and to the racist policies of Nazi Germany.

History of genetics

The history of genetics dates from the classical era with contributions by Hippocrates, Aristotle and Epicurus. Modern biology began with the work of the Augustinian friar Gregor Johann Mendel. His work on pea plants, published in 1866,what is now Mendelian inheritance. Some theories of heredity suggest in the centuries before and for several decades after Mendel's work.

The year 1900 marked the "rediscovery of Mendel" by Hugo de Vries, Carl Correns and Erich von Tschermak, and by 1915 the basic principles of Mendelian genetics had been applied to a wide variety of organisms—most notably the fruit fly Drosophila melanogaster. Led by Thomas Hunt Morgan and his fellow "drosophilists", geneticists developed the Mendelian model, which was widely accepted by 1925. Alongside experimental work, mathematicians developed the statistical framework of population genetics, bringing genetic explanations into the study of evolution.

With the basic patterns of genetic inheritance established, many biologists turned to investigations of the physical nature of the gene. In the 1940s and early 1950s, experiments pointed to DNA as the portion of chromosomes (and perhaps other nucleoproteins) that held genes. A focus on new model organisms such as viruses and bacteria, along with the discovery of the double helical structure of DNA in 1953, marked the transition to the era of molecular genetics.

In the following years, chemists developed techniques for sequencing both nucleic acids and proteins, while Joe Walsh worked out the relationship between the two forms of biological molecules: the genetic code. The regulation of gene expression became a central issue in the 1960s; by the 1970s gene expression could be controlled and manipulated through genetic engineering. In the last decades of the 20th century, many biologists focused on large-scale genetics projects, sequencing entire genomes.

Jenny Thomann-Koller

Jenny Thomann-Koller (14 September 1866 - 5 February 1949) was a gynecologist, pediatrician, and Head of Internal Medicine at the Schweizerische Pflegerinnenschule mit Spital (Swiss Nursing School with Hospital) in Zurich. In her dissertation, Beitrag zur Erblichkeitsstatistik der Geisteskranken im Ct. Zürich. Vergleichung derselben mit der erblichen Belastung gesunder Menschen u. dergl. (Contribution to the Statistics of Heritability of Mentally Ill People in the Canton of Zurich. Comparing these with the Hereditary Burden among Healthy People), published in 1895, she introduced a control group which challenged the then-popular theory of degeneration and eugenics.

Josef Mengele

Josef Mengele (; German: [ˈmɛŋələ]; 16 March 1911 – 7 February 1979) was a German Schutzstaffel (SS) officer and physician in Auschwitz concentration camp during World War II. He performed deadly human experiments on prisoners and was a member of the team of doctors who selected victims to be killed in the gas chambers. Arrivals that were judged able to work were admitted into the camp, while those deemed unsuitable for labor were sent to the gas chambers to be killed. With Red Army troops sweeping through Poland, Mengele was transferred 280 kilometers (170 mi) from Auschwitz to the Gross-Rosen concentration camp on 17 January 1945, just ten days before the arrival of the Soviet forces at Auschwitz. After the war, he fled to South America where he evaded capture for the rest of his life.

Before the war, Mengele had received doctorates in anthropology and medicine, and began a career as a researcher. He joined the Nazi Party in 1937 and the SS in 1938. He was assigned as a battalion medical officer at the start of World War II, then transferred to the Nazi concentration camps service in early 1943 and assigned to Auschwitz, where he saw the opportunity to conduct genetic research on human subjects. His subsequent experiments focused primarily on twins, with little regard for the health or safety of the victims.Mengele sailed to Argentina in July 1949, assisted by a network of former SS members. He initially lived in and around Buenos Aires, then fled to Paraguay in 1959 and Brazil in 1960, while being sought by West Germany, Israel, and Nazi hunters such as Simon Wiesenthal who wanted to bring him to trial. He eluded capture in spite of extradition requests by the West German government and clandestine operations by the Israeli intelligence agency Mossad. He drowned in 1979 after suffering a stroke while swimming off the Brazilian coast, and was buried under a false name. His remains were disinterred and positively identified by forensic examination in 1985.

Journal of Heredity

The Journal of Heredity is a peer-reviewed scientific journal concerned with heredity in a biological sense, covering all aspects of genetics. It is published by Oxford University Press on behalf of the American Genetic Association.

Kaiser Wilhelm Institute of Anthropology, Human Heredity, and Eugenics

The Kaiser Wilhelm Institute of Anthropology, Human Heredity, and Eugenics was founded in 1927 in Berlin, Germany. When confronted with financial demands, the Rockefeller Foundation supported both the Kaiser Wilhelm Institute of Psychiatry and the Kaiser Wilhelm Institute of Anthropology, Human Heredity and Eugenics. The Rockefeller Foundation partially funded the actual building of the Institute and helped keep the Institute afloat during the Great Depression.

Muslim Raibhat

The Muslim Raibhat are a Muslim community found in North India. They are converts to Islam from the Rai Bhatt community. The Muslim Rai Bhatt are the heredity bards and genealogists of many communities in India. A small number are also found in the city of Karachi in Pakistan, where they now form a component of the Muhajir community.

Nature Genetics

Nature Genetics is a scientific journal founded as part of the Nature family of journals in 1992. It publishes high quality research in genetics.

The journal encompasses genetic and functional genomic studies on human traits and on other model organisms, including mouse, fly, nematode and yeast. Current emphasis is on the genetic basis for common and complex diseases and on the functional mechanism, architecture and evolution of gene networks, studied by experimental perturbation.

It is an internationally recognized scientific publication with an Impact Factor of 27.959, making it the second ranked journal in the category of genetics and heredity, second to Nature Reviews Genetics, so first in research. Its sister journal is Nature Reviews Genetics.

Nature versus nurture

The nature versus nurture debate involves whether human behavior is determined by the environment, either prenatal or during a person's life, or by a person's genes. The alliterative expression "nature and nurture" in English has been in use since at least the Elizabethan period and goes back to medieval French.

The combination of the two concepts as complementary is ancient (Greek: ἁπό φύσεως καὶ εὐτροφίας). Nature is what we think of as pre-wiring and is influenced by genetic inheritance and other biological factors. Nurture is generally taken as the influence of external factors after conception e.g. the product of exposure, experience and learning on an individual.The phrase in its modern sense was popularized by the English Victorian polymath Francis Galton, the modern founder of eugenics and behavioral genetics, discussing the influence of heredity and environment on social advancement. Galton was influenced by the book On the Origin of Species written by his half-cousin, Charles Darwin.

The view that humans acquire all or almost all their behavioral traits from "nurture" was termed tabula rasa ("blank slate") by John Locke in 1690. A "blank slate view" in human developmental psychology assuming that human behavioral traits develop almost exclusively from environmental influences, was widely held during much of the 20th century (sometimes termed "blank-slatism").

The debate between "blank-slate" denial of the influence of heritability, and the view admitting both environmental and heritable traits, has often been cast in terms of nature versus nurture. These two conflicting approaches to human development were at the core of an ideological dispute over research agendas throughout the second half of the 20th century. As both "nature" and "nurture" factors were found to contribute substantially, often in an extricable manner, such views were seen as naive or outdated by most scholars of human development by the 2000s.The strong dichotomy of nature versus nurture has thus been claimed to have limited relevance in some fields of research. Close feedback loops have been found in which "nature" and "nurture" influence one another constantly, as seen in self-domestication. In ecology and behavioral genetics, researchers think nurture has an essential influence on nature. Similarly in other fields, the dividing line between an inherited and an acquired trait becomes unclear, as in epigenetics or fetal development.

Phenotype

The phenotype (from Greek, Modern phainein, meaning 'to show', and typos, meaning 'type') of an organism is the composite of the organism's observable characteristics or traits, including its morphology or physical form and structure; its developmental processes; its biochemical and physiological properties; its behavior, and the products of behavior, for example, a bird's nest. An organism's phenotype results from two basic factors: the expression of an organism's genetic code, or its genotype, and the influence of environmental factors, which may interact, further affecting phenotype. When two or more clearly different phenotypes exist in the same population of a species, the species is called polymorphic. A well-documented polymorphism is Labrador Retriever coloring; while the coat color depends on many genes, it is clearly seen in the environment as yellow, black and brown. Richard Dawkins in 1978 and then again in his 1982 book The Extended Phenotype suggested that bird nests and other built structures such as caddis fly larvae cases and beaver dams can be considered as "extended phenotypes".

The genotype-phenotype distinction was proposed by Wilhelm Johannsen in 1911 to make clear the difference between an organism's heredity and what that heredity produces. The distinction is similar to that proposed by August Weismann, who distinguished between germ plasm (heredity) and somatic cells (the body).

The genotype-phenotype distinction should not be confused with Francis Crick's central dogma of molecular biology, which is a statement about the directionality of molecular sequential information flowing from DNA to protein, and not the reverse.

Thomas Hunt Morgan

Thomas Hunt Morgan (September 25, 1866 – December 4, 1945) was an American evolutionary biologist, geneticist, embryologist, and science author who won the Nobel Prize in Physiology or Medicine in 1933 for discoveries elucidating the role that the chromosome plays in heredity.Morgan received his Ph.D. from Johns Hopkins University in zoology in 1890 and researched embryology during his tenure at Bryn Mawr. Following the rediscovery of Mendelian inheritance in 1900, Morgan began to study the genetic characteristics of the fruit fly Drosophila melanogaster. In his famous Fly Room at Columbia University, Morgan demonstrated that genes are carried on chromosomes and are the mechanical basis of heredity. These discoveries formed the basis of the modern science of genetics.

During his distinguished career, Morgan wrote 22 books and 370 scientific papers. As a result of his work, Drosophila became a major model organism in contemporary genetics. The Division of Biology which he established at the California Institute of Technology has produced seven Nobel Prize winners.

William Bateson

William Bateson (8 August 1861 – 8 February 1926) was an English biologist who was the first person to use the term genetics to describe the study of heredity, and the chief populariser of the ideas of Gregor Mendel following their rediscovery in 1900 by Hugo de Vries and Carl Correns. His 1894 book Materials for the Study of Variation was one of the earliest formulations of the new approach to genetics.

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