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It’s a boy! Or is it? Variability in human gender development. Cynthia J. Gill, Ph.D. University of Texas. Androgen-receptor deficient male (TFM). Sex determination and differentiation Objectives Distinguish gender as defined by various criteria.
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It’s a boy! Or is it? Variability in human gender development. Cynthia J. Gill, Ph.D. University of Texas
Sex determination and differentiation • Objectives • Distinguish gender as defined by various criteria. • State the critical factors for reproductive system differentiation. • Predict the result of variations during development.
Chromosomal sex (genetic sex) XX or XY, Y has SRY gene Gonadal sex (gametic sex) ovary or testis (eggs or sperm) Hormonal sex estrogen or testosterone Morphological sex Behavioral sex (internal and external genitalia, 2° sex characteristics) (brain morphology, behavior) Gender identity “I am male” or “I am female”
Cascade of events in development of male
Synthesis pathway for steroid hormones 5 reductase
Sex differentiation: cascade event rules • SRY gene determines testes development • Testes make testosterone and MIS • Testosterone differentiates Wolffian ducts • MIS inhibits Müllerian duct differentiation • Testosterone masculinizes external genitalia but full differentiation is by DHT
Identify the sex determination and/or differentiation: XY XX XY with absent SRY gene XX with SRY gene XY with no functional androgen (T & DHT) receptor XX with hypersecretion of testosterone XY with no 5 reductase enzyme Gonads: testes or ovaries? Internal genitalia: Wolffian or Müllerian duct development? External genitalia: male-like or female-like?
How would you decide who is ‘male’ and who is ‘female’ for gender-separate sports events in the Olympics?
Sexual Differentiation: gonads • Every embryo initially has two undifferentiated primordial gonads • The Y chromosome directs development into male gonads, testes • The absence of the Y chromosome causes development into the female gonad, or ovary • Sexual differentiation: Internal Genitalia • Each embryos has two sets of internal organs, the Wolffian and the Mullerian ducts • The Wolffian ducts are the precursors of the male internal genitalia, and develop under the influence of testosterone • The Mullerian ducts are the precursors of the female genitalia and develop unless Mullerian inhibiting substance is present
Sexual differentiation: External Genitalia • Both male and female embryos have protruding tufts of flesh called the genital tubercle, urethrogenital folds, and labioscrotal swellings • In the male body, testosterone is converted to dihydrotestosterone, the androgen that converts the embryonic external genitalia into the penis and scrotum • In the absence of dihydrotestosterone, the external genitalia become female