8. Sex Determination 2010 sm

8. Sex Determination 2010 sm - Genetic Sex Determination...

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Genetic Sex Determination
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Sex is determined by the heat of male partner during intercourse….. Aristotle (384-322 B.C.) Courtesy of Humphrey Yao
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Sex Differentiation: a favorite topic for philosophers and scientists 8th BC Homer: Conception is influenced by the wind, north for males and south for females…at least in sheep 130-200 A.D. Galen: Semen from left testis makes females, right makes males. A mixture produces hermaphrodites. 1677 Anton van Leeuwenhoek: sperm 1827 Carl Ernst von Baer: ovum 1902 Clarence McClung: the “Accessory chromosome” 1947 Alfred Jost: differentiation of the reproductive tract 1949 Barr & Bertram: discovery of the Barr bodies 1959 Welshons & Russell: the role of the Y chromosome 1991 Lovell-Badge et al: discovery of the SRY gene Courtesy of Humphrey Yao
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The Jost Paradigm Genetic Sex Gonadal Sex Phenotypic Sex Switches G enetic S ex D etermination Sex Chromosomes E nvironmental S ex D etermination Temperature, social cues, etc Courtesy of Humphrey Yao
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Mammals Birds Crocodiles Turtles Snakes Amphibians Fish Both Both GSD Both ESD GSD GSD Evolution of Sex Determination Mechanisms Courtesy of Humphrey Yao
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Evolution of Sex Determination Mechanisms
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Sex Determination Earthly Venus - offspring of different races – Pierre Louis Moreau de Maupertuis – Venus physique / The Earthly Venus – La Haye, 1745 Speculation on organismal adaptation to environment 100 yrs before Darwin Examined debate on source of humans – Sperm – Egg How did he test this? Hint: della Porta
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Genetics of Sex Determination rediscovery of Mendel /others suggested genetic factor 1902 Clarence McClung: the “Accessory chromosome” 1959 Welshons & Russell: the role of the Y chromosome 1991 Lovell-Badge et al: discovery of the SRY gene
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Gonadal Differentiation Kim & Capel, Develop Dynamics 235:2292–2300, 2006 http://gg.bu.edu/people/faculty/albrecht.htm
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Human Primary Sex Determination 1. gonadal determination 2. chromosomal a. female = XX b. male = XY 3. number of X chromosomes not important 4. presence of the Y is critical
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Y Chromosome Represents 2% of haploid complement differ between species in size and gene content Contains over 200 genes Contains over 50 million base pairs, of which approximately 50% have been determined Genes for Sex determination – Histocompatibility – Spermatogenesis – Growth – Cancer
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X Chromosome Contains over 1400 genes ~5% of the haploid genome Contains over 150 million base pairs approximately 95% have been determined sex linked genes in the X chromosome all these genes will be dominant no opposing genes in the Y chromosome freely expressed in the organisms phenotype hairy ears in old age. Sex Linked Characteristics Red-Green color blindness Hemophilia - prevents the clotting of the blood Hairy ears in men through advancing age
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X Inactivation Forms the Barr Body Condensation of some of the genes on one of the X chromosome • Why?
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