Sexual Determination and Differentiation
Differentiation of
genitalia
differentiation = anatomical development; process by which cells develop (differentiate) into specific cell types.
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Developmental
Event/Condition |
Normal
Female Development |
Normal
Male Development |
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Chromosomal
Sex |
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Presence
of TDF gene? |
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Anlagen
for gonads |
bipotential
germinal ridge |
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Expression
of TDF gene? |
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Gonad
Development |
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Gonad
Hormone Production |
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Anlagen
for male accessory organs |
Wolfian
duct |
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Wolfian
duct exposure to testosterone? |
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Wolfian
duct development? |
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Anlagen
for female accessory organs |
Mullerian
duct |
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Mullerian
duct exposure to MIH? |
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Mullerian
duct development? |
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Anlagen
for external genitalia |
Genital
skin containing 5-alpha-reductase |
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Genital
skin exposure to DHT? |
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External
genitalia development |
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Anlagen — primordial tissue: the first accumulation of cells in an embryo which constitutes the beginning of a future tissue or organ.
MIH = Mullerian Inhibitory Hormone (AKA Mullerian Regression Factor)
DHT = 5-alpha-dihydrotestosterone
What enzyme catalyzes the conversion of testosterone to the Òsuper testosteroneÓ, 5-alpha-dihydrotestosterone (DHT)?
Propecia (finasteride): mechanism of action—
potential developmental side effects—
Sexual differentiation is a demonstration of organizational effect of hormones. If after birth a male is castrated the genitalia will remain masculine. It also illustrates critical periods—no amount of testosterone after differentiation of these structures along female lines will convert them into the masculine form.
Sexual Anomalies (see Table)
Male (XY) lack of
exposure to TDF, MIH, testosterone or DHT during critical periods of
development:
TFM (AKA androgen insensitivity):
side note: chromosomal location of androgen receptor—
Secondary sex characteristics
Breast development—
Pubic hair—
LH, FSH levels—
Testosterone levels—
incidence—
5-alpha-reductase deficiency:
Gender assignment at birth—
Gender identity—
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Chromosome (Total
#, Sex) |
Syndrome/De-fect |
gonads |
accessory
sexual organs |
external
genitalia |
secondary
sex characteristics |
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46, XY |
Lack of TDF |
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46, XY |
Testicular
Feminization Mutation (TFM); absence of androgen receptors |
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46, XY |
Lack of MIH or
defective MIH receptors |
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46, XY |
5-alpha-reductase
deficiency (guevedoces) |
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46, XX |
Fetal exposure to
exogenous steroids with androgen effects |
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46, XX |
Fetal exposure to
endogenous androgens (Congenital Adrenal Hyperplasia) |
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45, XO |
Turner's syndrome (monosomy) |
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47, XXY |
Klinefelter
syndrome (trisomy) |
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47, XYY |
trisomy |
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