Lecture 9 notes

Lecture 9 notes - Lecture #9- Sex Determination and...

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Lecture #9- Sex Determination and Differentiation (ch 7 p. 164-174, ch 11 p. 262) I. Sex Determination in Humans A. Y chromosome designated maleness in humans normal: XY = males, XX =Females abnormal: XXY = Male, XO = Females B. The male gamete determines the sex of the offspring (draw Punnett square) female = homogametic since she can only contribute an X to the gamete male = heterogametic since he can contribute an X or a Y C. Expect equal numbers of male and female offspring = sex ratio At birth, however, there are slightly more males than females (1.06 male/female) The ratio approaches 1:1 in adults due to the high death rate in males. Some factors include deleterious X-linked genes and the high rate of lethal accidents for males from age 15-35 years (is the leading cause of death for this group) world = 6,512,822,690 (look at clock link) 102 males/100 females II. Sex Differentiation: becoming male or female A. Normal Male and female development 1. Early Embryogenesis (fig. 7.12, Handout) male and female reproductive ducts: male = Wolffian female = Mullerian development (handout) Testis development is initiated under the control the Y chromosome genes, with no Y chromosome, no testis development occurs in females, ovaries develop instead. Note the effects on the ducts. 2. Phenotypic Sex Development involves a different pathway and different genes than gonad (testes and ovaries) development. Once formed, the testis secretes hormones that act together with other gene products to control sexual development. male = Y chromosome genes, single X, genes on autosomes. Dihydroxytestosterone (DHT) = an androgen that testosterone is converted into that directs male external genitalia development.
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females = no Y chromosome, 2 XX, genes on autosomes B. When the Phenotypic Sex doesn't match the Genotypic Sex. 1. Androgen insensitivity (XY female) Mutation in a receptor (androgen receptor) on cells that makes the cells unable to respond to Testosterone and DHT. MIH still causes the Mullerian ducts to be degraded. With no ability to respond to
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Lecture 9 notes - Lecture #9- Sex Determination and...

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