09.22.11 - Lecture 6. The ordered nature of chromosomes,...

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Lecture 6. The ordered nature of chromosomes, genetic linkage confirmed by mapping Readings: Chapt 4, 121-137
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What to bring to Exam I? 1. #2 pencil. 2. Calculator. 3. Your STUDENT ID # and DISCUSSION SECTION NUMBER. Important: If you are in Discussion Sections 2-11 your exam is in Nat Sci Aud. If you are in Discussion Sections 12-18 your exam is in Chem 1210
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Calvin Bridges discovery of sex determination in Drosophila X X w- X w- X w+ Y X w+ X w- X w- Y 1/2 1/2 C. Bridges Observation: 1/2000 females had white eyes 1/2000 males had red eyes C. Bridges Hypothesis: ~1/2000 tries, X and Y chromosomes do not segregate properly during meiosis. (nondisjunction)
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2 n =2 Nondisjunction zygotes zygotes
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Predicted genotypes and phenotypes under normal segregation and nondisjunction in Bridge’s expt. C. Bridges Hypothesis: ~1/2000 tries, X and Y chromosomes do not segregate properly during meiosis. X w+ Y X w- X w+ Y normal NDJ XX nothing Xw-Xw- Xw+ =dead Xw-Xw-Y Xw+O OY= dead Male sterile Female white
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Comparison of sex determining mechanisms in humans and Drosophila Drosophila XXY normal female XO sterile male YO dead XXX metafemale (mostly dead) human XXY sterile male (Klinefelter) XO sterile female (Turner) YO dead XXX mostly normal females
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Sex determination in Drosophila
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Nematode C. elegans
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Clicker Question: Assume that there is a role of nondisjunction in the production of rare males in C. elegans . Can you devise a mode of chromosomal sex determination, which explains the data on C. elegans ratios of hermaphrodites to males and results of crosses between hermaphrodites and males ? a). Hermaphrodites are XO, males are XX. Because hermaphrodites self they remain XO. Males are produced by rare non-disjunction in XO hermaphrodites. b). Hermaphrodites are XY, males are XX. Because hermaphrodites self they remain XY. Males are produced by rare non-disjunction in XY hermaphrodites. c). Hermaphrodites are XX, males are XO. Males are produced by rare non-disjunction in XX hermaphrodites during meiosis I \ d). Hermaphrodites are XX, males are XO. Males are produced by rare non-disjunction in XX hermaphrodites during meiosis I or II
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Sex determination in birds and butterflies
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Lecture 6. The ordered nature of chromosomes, genetic linkage confirmed by mapping Genetic map of Pisum sativum
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Concepts 1.Genes on the same chromosome display linkage which violates Mendel’s law of independent assortment. 1.Recombination
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This note was uploaded on 01/19/2012 for the course BIOLOGY 305 taught by Professor Kumar during the Fall '11 term at University of Michigan.

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09.22.11 - Lecture 6. The ordered nature of chromosomes,...

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