3 Sex determination and differentiation ObjectivesDistinguish gender as defined by various criteria.State the critical factors for reproductive system differentiation.Predict the result of variations during development.
4 Chromosomal sex (genetic sex) XX or XY, Y has SRY geneGonadal sex (gametic sex)ovary or testis (eggs or sperm)Hormonal sexestrogen or testosteroneMorphological sexBehavioral sex(internal and external genitalia,2° sex characteristics)(brain morphology, behavior)Gender identity“I am male” or “I am female”
7 Synthesis pathway for steroid hormones 5 reductase
8 Sex differentiation: cascade event rules SRY gene determines testes developmentTestes make testosterone and MISTestosterone differentiates Wolffian ductsMIS inhibits Müllerian duct differentiationTestosterone masculinizes external genitalia but full differentiation is by DHT
9 Identify the sex determination and/or differentiation: XYXXXY with absent SRY geneXX with SRY geneXY with no functional androgen (T & DHT) receptorXX with hypersecretion of testosteroneXY with no 5 reductase enzymeGonads: testes or ovaries?Internal genitalia: Wolffian or Müllerian duct development?External genitalia: male-like or female-like?
10 How would you decide who is ‘male’ and who is ‘female’ for gender-separate sports events in the Olympics?
13 Sexual Differentiation: gonads Every embryo initially has two undifferentiated primordial gonadsThe Y chromosome directs development into male gonads, testesThe absence of the Y chromosome causes development into the female gonad, or ovarySexual differentiation: Internal GenitaliaEach embryos has two sets of internal organs, the Wolffian and the Mullerian ductsThe Wolffian ducts are the precursors of the male internal genitalia, and develop under the influence of testosteroneThe Mullerian ducts are the precursors of the female genitalia and develop unless Mullerian inhibiting substance is present
14 Sexual differentiation: External Genitalia Both male and female embryos have protruding tufts of flesh called the genital tubercle, urethrogenital folds, and labioscrotal swellingsIn the male body, testosterone is converted to dihydrotestosterone, the androgen that converts the embryonic external genitalia into the penis and scrotumIn the absence of dihydrotestosterone, the external genitalia become female