GENE20001 Lecture Notes - Lecture 5: Mals, Wild Type, Zygosity
Sexual dimorphism and sex chromosomes
e.g. humans, drosophila
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Female XX homogametic (1 type of egg)
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Male XY heterogametic (2 types of sperm)
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XY
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e.g. grasshopper, firefly, many insects
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Female XX homogametic (1 type of egg)
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Male XO heterogametic (2 types of sperm)
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XO
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e.g. birds, moths, butterflies, reptiles, some fish
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Male ZZ homogametic (1 type of sperm)
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Female ZW heterogametic (2 types of egg)
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ZW
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3 main sex chromosome systems
Most genes on X have no counterpart on Y.
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Much of the Y is genetically inert
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More genes on X than Y
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Dominance/recessiveness only in females (XX) for genes on X
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No dominance/recessive interactions in male (XY; hemizygous) for genes on X.
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Testcross to map X-linked genes
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Y-linked inheritance e.g. hair on ears
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The XY system
5 Sex linkage
Wednesday, 12 March 2014
11:11 PM
Genetics Page 1
Document Summary
Male xy heterogametic (2 types of sperm) e. g. grasshopper, firefly, many insects. Male xo heterogametic (2 types of sperm) e. g. birds, moths, butterflies, reptiles, some fish. Most genes on x have no counterpart on y. Dominance/recessiveness only in females (xx) for genes on x. No dominance/recessive interactions in male (xy; hemizygous) for genes on x. X-linked inheritance e. g. haemophilia (blood clot failure) inheritance: more frequent in males, no direct father-son transmission, skips one generation. Morgan"s experiments with white-eye mutant fly: w+ normal eye, w white eye. P: wild type female x white eye male. P: white eye female x wild type male. F2: all female wild, half male wild, half male white. F2: half female wild, half female white, half male wild, half male white. P: wild type female produces x+ gametes only. ^^^these pictures are disgusti(cid:374)g i"ll tr(cid:455) a(cid:374)d e(cid:454)tract co(cid:374)te(cid:374)t out of the(cid:373).
