Lecture 4 - Intro to population genetics

Lecture 4 - Intro to population genetics - 1 Lecture 4 -...

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1 Lecture 4 - Introduction to Theoretical Evolutionary Biology I. VERY brief historical background: See article by Betty Smocovitis - The view of biological species (and the Universe) from antiquity was that species were fixed entities, stems from Aristotle and especially Plato, consistent with biblical account of Creation. - 1809: Lamarck proposes first formal, coherent theory of evolution. Salient features are multiple origins of living forms, life evolves from the simple to the complex, traits change by use and disuse (e.g., giraffe's neck), and acquired characters are heritable. - 1858: Darwin and Wallace present their papers on Evolution by Nat Seln to Linnean Society of London; each inspired by geographic variation, and read Malthus; Darwin particularly inspired by plant and animal breeding. - 1859 Origin published; Evolution per se ("transmutation") quickly accepted, NS as the mechanism not - Objections to Evol by NS: Fossil record, lack of intermediate forms; "utility of form", i.e., highly adapted and complex structures, e.g., the vertebrate eye; age of the Earth (calculated at ~25,000 yrs by Lord Kelvin); especially the putative mechanism of heredity, i.e., blending inheritance, as argued by Jenkin. Non-Darwinian theories of evolution 1. Neo-Lamarckism ; inheritance of acquired modifications. Darwin himself proposed inheritance of acquired characters; prevalent form of evolutionism in the late 19th century. Weismann (1893); embryologist, selectionist, proposed separate germ- line and soma, proposed chromosomes as the "seat of heredity", refuted inheritance of acquired characters. 2. Orthogenesis (popular among paleontologists): variation directed toward fixed goals, species evolves in a pre-determined direction, some argued that trends need not be adaptive, and the ultimate goal was extinction. No mechanism ever proposed. 3. Mutationism : Mendel rediscovered ca. 1900, clearly establishing the discrete nature of heredity. From that first principle, the Ms argued that mutations with discrete, large effects drove evolution, small continuous variation unimportant. In the early 20th century selectionists were represented by the "Biometricians", who were (as it happens) the fathers of modern statistics. They focused on continuously distributed variation in the population and made statistical arguments for natural selection as the mechanism of evolution. The geneticists were experimentalists, among them De Vries ( Oenothera ),
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2 Bateson, and Morgan ( Drosophila ). The initial mutations they focused on were mutations of large effect, e.g., eye color in flies. - 1910, Morgan conclusively demonstrated that chromosomes were the seat of heredity. Johannsen's experiment with beans showed that selection could operate among "strains" within a population but not produce an individual outside the range of the population, confirmed Jenkin's argument. -
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This note was uploaded on 06/08/2011 for the course PCB 4674 taught by Professor Baer during the Fall '08 term at University of Florida.

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Lecture 4 - Intro to population genetics - 1 Lecture 4 -...

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