Mendelian Genetics |
from Gregor Johann Mendel (1822–1884), an Austrian monk, experimenting on common garden pea |
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1865 – Laws of Particulate Inheritance (dissertation) |
describing the principles of transmission of genetic material from one generation to the next |
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1900 – rediscovery of Mendel's law |
Carl Correns (1864–1933), Hugo de Vries (1948–1935), Erich Tschermak |
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1901 – William Bateson (1861–1926), British geneticist |
produced the first evidence of inheritance with experiments with chickens |
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coincidentally, provided the classical definition of genetics as a field of study, i.e. as a science dealing with heredity and variation seeking to discover laws governing similarities and differences in individuals related by descent |
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leading promoter of Mendelian genetics vs Biometricians (biological mathematicians) in the first two decades of the 20th century |
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coined technical terms such as homozygote, heterozygote, allelomorph |
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1906 – Willhelm Johanssen (1857–1927), Danish botanist |
introduced the terms gene, genotype, and phenotype |
Population Genetics |
study of Mendelian genetics in populations of plants and animals |
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basic foundation: Hardy-Weinberg Law |
1908 – Godfrey Harold Hardy (1877–1947), English mathematician |
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Willhelm Weinberg (1862–1937), German physician |
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usually limited to the inheritance of qualitative characters which are influenced by only a small number of (major) genes |
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study why characteristics become fixed or continue to exhibit variation in natural populations |
importance: design of selection strategies to increase frequency of desirable genes or examples: |
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Meishan pigs for prolificacy – around 12 offspring |
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dwarf gene in poultry |
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Booroola gene in sheep for multiple births |
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double muscling gene in Pietrain pigs and Belgian blue cattle |
Quantitative Genetics |
conceptually the most difficult of the three areas |
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hypothesis: many genes contribute to expression of traits |
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effects of individual genes can seldom be seen or measured, e.g. milk yield, growth rate, litter size |
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complications due to random influence of the environment and other non-genetic factors mask the combined effects of many genes influencing the trait |
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quantitative genetics is the most important of the three areas because: |
response to selection for quantitative traits generally has much more potential monetary value than those for simply-inherited traits |
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Ronald Aylmer Fisher (1890–1962), British statistician and geneticist, and Sewall Green Wright (1889–1988), American geneticist |
reconciled Mendelians and biometricians |
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Mendelian results: in terms of frequencies of genotypes and phenotypes |
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biometricians results: in terms of correlations and regressions (before rediscover of Mendel's laws) |
e.e. Francis Galton (1822–1911), Karl Pearson (1857–1936) |
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Fischer and Wright: demonstrated that Mendelian frequencies were the basis of biometrical correlations |
