04-sexual%20differentiation - Sex determination and...

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Sex determination and differentiation
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Sex determination and differentiation
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Sexual dimorphisms and how they get there.
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Sexual dimorphisms Dimorphism : the existence of two different forms (as of color or size) of a species especially in the same population <sexual dimorphism > - robins Behaviors can be sexually dimorphic, too - aggression Dimorphisms are not necessarily absolute. There is often overlap between males and females
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What are some sexual dimorphisms?
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Just talking about sexual dimorphism can influence (or create?) it.
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Men versus women: Math performance 1. No Gender Difference (ND) Condition: A meta-analysis across multiple countries revealed that males and females performed equally well on math tests. 2. Standard Stereotype Threat (S) Condition: The role of the female body in the arts was discussed with relation to women’s identity. 3. Genetic (G) Condition: Males perform 5 percentile points better on math tests than women because of some genes that are found on the Y chromosome. 4. Experiential (E) Condition: Males perform 5 percentile points better on math tests than women because teachers biased their expectations during early school formative years. Math Test Read Text Math Test Four different kinds of text:
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Dar-Nimrod, I. and Heine, S.J. Exposure to scientific theories affects women’s math performance. Science , 314: 435, 2006.
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Sex and gender: Are they different? If so, how?
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Why have two sexes? Having two sexes really complicates things and takes up a tremendous amount of time and energy. Isn’t parthenogenesis good enough for us? (parthenogenesis: eggs develop without fertilization seen in some types of fish, amphibians, and reptiles)
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How do we get to be males and females?
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XX Mammalian sex determination X Y SRY gene testis testis determination factor bipotential gonad (medulla) testis bipotential gonad (medulla) testis determination factor XX + SRY (transgenic ) X Y- SRY (knockout ) ovary bipotential gonad (cortex) No SRY gene ovary bipotential gonad (cortex) No SRY gene
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Undifferentiated internal plumbing immature gonad note: two sets of pipes, one and one
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The fetal testis produces two substances which determine whether the internal plumbing will be male or female (or neither or both). Mullerian inhibitory hormone (a peptide) acts on the female plumbing (Mullerian ducts) and causes it to atrophy. Testosterone (a steroid) acts on the male plumbing (Wolffian ducts) and makes them grow. Defeminization Masculinization
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Internal plumbing If the testes produce testosterone, but not MIH, the fetus will develop both and internal plumbing If the testes produce MIH, but not testosterone, the fetus will develop neither nor internal plumbing testosterone (stimulates growth of male plumbing) no MIH means female plumbing develops Mullerian inhibitory hormone (inhibits growth of female plumbing)
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Differentiation of the external plumbing testis 5α-DHT testosterone ovary nada note: one set of tissues, either or , but not both
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In the absence of testes, the internal and external genitalia develop in a normal female pattern. Nothing else is necessary. The default is female.
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  • Spring '08
  • GeorgeWade
  • Sexual dimorphism, Sexual differentiation

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