140-S08-Mar31

140-S08-Mar31 - A second practice problem set (with...

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A second practice problem set (with answers) is on the course website. The review session for the second midterm is on Thursday evening, April 10, from 7-9pm in ROOM 141 GIANNINI HALL
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GSD : genotypic sex determination Segregation of alleles (genes) determines sex best for generating 1:1 sex ratios onwards with: Amazing variety of mechanisms the most rapidly evolving aspect of developmental programming)
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XX (±Y) females X(±Y) males What about X-chromosome number matters? …again, genetic exceptions to the rule provide the answer For fruit flies: absolute number: 1=male, 2 or more = female odd vs. even (paired?) XX X=male? number relative to ploidy (non-sex chromosomes) ? X AA male, but X A female? X:A ratio
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XX(±Y) AA X:A = 1, female X(±Y) AA X:A = 0.5, male XX(±Y) AAA X:A = 0.67, intersex (phenotypic mos aic ) XXX AAA X:A= 1, female ( jumbo ) ( dead ) For fruit flies: Bridges' "exceptional" female: female Progeny from X A X:A=1, What about: how could he know???
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XX AA zygote --> XX AA cells / X AA cells recall that: X-chromosome loss generates gynandromorphs GENETIC MOSAICS revealed the sex of X A cells (nonmosaic XA animals never reach the sexually dimorphic (adult) stage) ( XXAA ) Female (X AA) Male ( XXAA ) Female (X A) Female XXAA zygote --> XX AA cells/ XA cells (loss of an entire haploid set ) (genetic "markers" allowed him to infer the genotypes)
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XX AA X:A = 1, female X AA X:A = 0.5, male XX(±Y) AAA X:A = 0.67, intersex XXX AAA X:A= 1, female (large) X A X:A=1, (dead) female GSD by X:A ratio (balance)
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by X:A ratio (balance) What is it about ploidy changes that affects the way that X-chromosome dose determines sex? "Obviously":
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This note was uploaded on 08/01/2008 for the course MCB 140 taught by Professor Urnov during the Spring '08 term at Berkeley.

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140-S08-Mar31 - A second practice problem set (with...

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