352SLecture05_S11 - Genetics and Evolution Lecture#5 Todays...

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1 Genetics and Evolution: Lecture #5 Today’s Topics 1. X and Y Chromosomes 2. Dosage Compensation 3. Sex-linked Genes Readings: Pierce, pgs. 81 - 91 The XX-XY System Females are the homogametic sex Males are the heterogametic sex Figure 4.4 Things to Note : 1. Insures equal sex ratios at birth. 2. Don’t like your sex? Blame your Dad!
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2 What Determines Maleness? Two possibilities: 1. The presence of the Y-chromosome 2. The absence of a second X-chromosome Phenotypes of sexual aneuploids. - Turner Syndrome: XO individuals are female - Klinefelter Syndrome: XXY, XXXY and XXXXY individuals are male The Y-Chromosome Y-chromosome: Smaller than the X-chromosome About 75 functional genes Pseudoautosomal regions. Figure 4.5 The Y-Chromosome What exactly IS it about the Y-chromosome? SRY gene discovered in 1990. - SRY = “Sex determining region Y” - TDF = “testes-determining factor” Sex reversed phenotypes: - XX males – SRY present on X - XY females – SRY missing from Y
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