Lecture12Notes - Last time Meiosis How chromosomes are...

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10/19/10 1 Mendelian Genetics Principles of Biology Lecture 12 Prof. David Fitch Last time: Meiosis How chromosomes are inherited Process makes haploid gametes from diploid organisms Produces variation among gametes Homologous chromosomes (maternal and paternal copies of the same chromosome) are segregated into different daughter cells during Meiosis I – Different ( nonhomologous ) chromosomes are assorted independently into the daughter cells during Meiosis I – Crossing-over between non-sister chromatids in Prophase I Fertilization restores the diploid state in the zygote Fertilization also produces different chromosome combinations Variation due to meiosis Segregation of homologous chromosomes and independent assortment of nonhomologous chromosomes into gametes Number of different types of gametes = 2 n Possibility 1 Two equal y probable arrangements of chromosomes at metaphase I Possibility 2 Metaphase I Daughter cel s Combination 1 Combination 2 Combination 3 Combination 4 Fertilization also produces variation The number of different combinations of diploid progeny (zygotes) produced by random fertilization = n(sperm types) x n(egg types) = 2 n x 2 n . n +n 2n n n zygote How are traits inherited? Typical genetics experiment – Green disappears in the second generation – Green reappears in the third generation – Hence, traits are not inherited from their parents, but factors that determine the traits are Charles Darwin vs . August Weissman Darwin (1868): "pangenesis" – "gemmules" produced by the body influence gametes – blending inheritance – Galton (1869-70) showed this does not occur via blood Weissman: "germ plasm theory" – germline passes heritable information without somatic influence – e.g., mutilations are not inherited Germ plasm: Soma: Reproductive elements: Body/organs:
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10/19/10 2 Rediscovery, confirmation, and elaboration of Mendel's work, 1900 Carl Correns Hugo de Vries Erich von Tschermak Johann "Gregor" Mendel Mathematician, started work in Brno (Brünn) Augustinian monastery ca. 1857 Brought statistical rigor to studies of inheritance (important for agriculture) Published results in lecture series, 1865 Model system for inheritance Mendel's MODEL SYSTEM, Pisum – can cross – can self – display discrete "traits" (variants) for "characters" (inherited features) – mating can be well- controlled • unlike hawkweed – many varieties Removed stamens Transferred pol en to carpel Seeds Plant seeds Al purple flowers F 1 P 0 Results Typical experiment – start with true- bred strain – F 1 all the same
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This note was uploaded on 11/03/2010 for the course BIOLOGY V23-0011-0 taught by Professor Fitch during the Fall '10 term at NYU.

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Lecture12Notes - Last time Meiosis How chromosomes are...

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