Sex Determination, Differentiation

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Sex Determination, Differentiation Development
Genetic Sex determined by chromosomes Gonadal
Sex determined by type of gonad Phenotypic Sex
Internal sex organs External genitalia Behavioral
sex
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Many Levels of Sex Determination
Chromosomal Sex
Gonadal Sex
Internal Sex Organs
External Sex Organs
Gender Identity
Gender Preference
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Chromosomal Sex Determination

• In Mammals
• Females are homogametic (XX)
• Males are heterogametic (XY)
• In birds and reptiles FEMALES are heterogametic
  sex F WZ M ZZ
• In fish males or females can be heterogametic or
  hermaphroditic
• In some lizards/turtles/alligators, the
  TEMPERATURE of egg incubation determines gender
  (temp/sex patterns vary by species)

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Temperature-Dependent Sex Determination

• Estrogen and Aromatase Hypothesis
• Aromatase activated at high temps
• Estrogen is produced and induces development
• of ovarian tissue
• Cell Proliferation and Maleness Hypothesis
• Sertoli cell proliferation induced by temperature
• leads to testes formation
• Did dinosaurs go extinct because of TDSD?

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Chromosomal Sex in HumansX and Y Chromosome
Inheritance
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Gonadal Sex Determination in Mammals
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7.14
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7.14ab
Indifferent Stages
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7.14c
Male Gonad
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7.14d
Male Gonad
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7.14e
Male Gonad
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7.14f
Female Gonad
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7.14g
Female Gonad
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7.14h
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Freemartin Effect in Cattle

• Sterile female twin of a male
• Occurs when placental blood supplies connect
• Can lead to testicular development in female
  twin
• Female reproductive tract completely regressed