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OutlineReview sex determination
Genetic syndromesSex-specific behaviors
sexual orientation and identityFlies
RodentsSheep
Humans
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Male developmentXY
SRY
Testes
Testosterone DHT anti-Mullerian hormone
Internal male external male structures structures
Mullerian ducts degenerate
Female developmentXX
Ovaries
No testosterone oranti-Mullerian hormone
Wolffian ducts degenerate;Internal and external female
structures
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Mutations that affect sexualphenotypes
5-alpha-reductase deficiency
Androgen insensitivity syndrome
Congenital adrenal hyperplasia
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XY individuals that lack 5 alpha reductase have testes that produceAMH and testosterone, but not DHT. AMH causes Mullerian ducts todegenerate, and testosterone induces Wolffian duct formation, butexternal genitalia are often female (or more female than male). Atpuberty massive amounts of testosterone cause the individuals sexorgans to change.
5 alpha reductaseX
5-alpha-reductase deficiency
X
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Androgen insensitivity syndrome (AIS)
XX
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XY individuals canʼt respond to androgens (testosterone or DHT).Testes form and produce AMH, so Mullerian ducts degenerate, buttissues donʼt respond to androgens, so Wolffian duct degeneratesand external genitalia develop as female structures.
5 alpha reductase
X X
Androgen insensitivity syndrome (AIS)
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Congenital adrenal hyperplasiaEnzyme that produces aldosterone and cortisol is
missing. XX individuals are masculinized.
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OutlineReview sex determination
Genetic syndromesSex-specific behaviors
sexual identity and orientationFlies
RodentsSheep
Humans
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Sexual orientationSexual identity
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Letʼs start with flies
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XX (X:A=1.0)
Sex lethal geneON
femaleFruitless
female behavior
XY (X:A=0.5)
Sex lethal geneOFF
maleFruitless
male behavior
Drosophila sexual development
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Drosophila Fruitless (Fru) is regulatedby alternate RNA splicing
Fru gene
male RNA splicing female RNA splicing
male Fru protein female Fru protein
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Fruitless controls malesexual behavior!
Fruitless mutant males lack courtshipbehavior.
Females that express male Fruitless exhibitmale courtship behavior.
Fruitless is a transcription factor
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Females expressing male Fruitlessexhibit male mating behavior.
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Male and female flies fightdifferently
males femalesbox push
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Male and female fighting behavioris regulated by Fruitless
males expressing female Fru push
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Dominance relationshipsare also regulated by Fruitless
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Fruitless is expressed in a subset of CNS neurons
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During early development testosterone regulates matingbehavior in rats
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Sexually dimorphic regions of the rat brain
Region larger in males
Region larger in females
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Sexual orientation in sheep
8% of rams are male oriented; i.e., theyattempt to mate with rams.
Male-oriented rams have a sexually dimorphicpart of the brain that is similar in size to that
in females.
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The sheep SDN is sexually dimorphic