It

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Its a boy! Or is it? Variability in human gender
development. Cynthia J. Gill, Ph.D. University
of Texas
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Androgen-receptor deficient male (TFM)
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• 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.

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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
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Gonad and internal genitalia differentiation
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Cascade of events in development of male
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Synthesis pathway for steroid hormones
5 ? reductase
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• 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

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• 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?
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How would you decide who is male and who is
female for gender-separate sports events in the
Olympics?
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Pathways of adrenal hormone synthesis.
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• 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

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• 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

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