2_Chromosomes

2_Chromosomes - 2) Inheritance of chromosomes and DNA We...

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1 1 2) Inheritance of chromosomes and DNA • 15.1 - 15.3 and 16.1 2 We now know that Mendel’s “hereditary factors” are located on chromosomes 3 Early studies of meiosis showed that the behavior of chromosomes parallels the behavior of Mendel’s “factors” • Both chromosomes and “factors” – Present in pairs in diploid cells – Segregate during meiosis – Halve their copy numbers during meiosis and double their copy numbers at fertilization 4 Thomas Hunt Morgan’s fruit fly experiments provided first strong evidence that genes are on chromosomes 5 Why fruit flies? • Easy to rear in lab • Short generation time (~10d) • Abundant offspring (100s per mating) • Only 4 pairs of chromosomes • Numerous mutation stocks now available 6
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2 P Generation F1 Generation F2 Generation P Generation F1 Generation F2 Generation P Generation F1 Generation Ova (eggs) Sperm F2 Generation Ova (eggs) Sperm Morgan’s explanation 9 What happens when genes are located on the same chromosome? • Morgan noticed that certain traits tended to be inherited together P Generation (homozygous) Parental-type offspring Double mutant (black body, vestigial wings) Recombinant (nonparental-type) offspring b b vg vg Double mutant (black body, vestigial wings) b b vg vg Ova Sperm TESTCROSS 965 Wild type (gray-normal) 944 Black- vestigial 206 Gray- vestigial 185 Black- normal Wild type (gray body, normal wings) b + b
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2_Chromosomes - 2) Inheritance of chromosomes and DNA We...

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