lecture 9 - 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 designates maleness in humans Males XY (XXY = Klinefelters) Females XX (XO = Turner’s Syndrome) B. Determination of the sex of offspring in humans is based on the presence or absence of the Y chromosome (draw Punnett square) female = homogametic XX (only has X’s) male = heterogametic XY C. Expect equal numbers of male and female offspring = sex ratio - At birth, more males than females -(1.06:1.0 male to female) -Approaches 1:1 in adults -X-linked disorders (recessive) that are lethal -High death rates in males ages 15-35 years of age due to accidents II. Sex Differentiation: becoming male or female A. Normal Male and Female Development 1. Early Embryogenesis (fig. 7.12, Handouts) 1. reproductive Ducts a. Male :; Wolffian duct b. Female: Mullerian duct 2. Gonad development ( Handout ) a. Testis development under control of Y chromosome 2. Phenotypic Sex Development involves a different pathway and different genes than gonad (testes and ovaries) development.
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