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primary and secondary sexual differentiation
- primary: involves only gonads where gametes are produced
- secondary: involves the overall appearance of the organism (mammary glands, external genitalia)
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protenor vs lygaeus mode of sex determination
- protenor: XX/XO
- •random distribution of X chromosomes into half of the male gametes
- •2 X in the zygote = female, 1 X = male
- lygaeus: XX/XY
- •female gametes all have X
- •male gametes either X or Y
- •zygotes with two X (homogametous) = female
- •zygotes with 1 X and 1 Y (heterogametous) = male
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when females are the heterogametic sex... notation and examples of species
- ZZ/ZW, moths, butterflies, most fish, reptiles, amphibians, one species of plants
- ZW=female
- ZZ=male
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syndrome with extra X or Y chromosome(s), features and karyotype examples
- Klinefelter syndrome
- usually 47,XXY... but can be 48,XXXY, 48,XXYY, 49,XXXXY, 49,XXXYY
- Tall, long arms and legs
- Underdeveloped testes and prostate, no facial hair
- Phenotypically male, infertile, slight breast enlargement, rounded hips
- Normal intelligence, slow learners
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syndrome and features of 45,XO karyotype
- Turner syndrome
- Female external genitalia, ovaries underdeveloped
- Short stature, skin flaps back of neck, flat breasts, broad chest
- Generally normal intelligence
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sex chromosome syndromes occur due to ___________ during _________.
sex chromosome syndromes occur due to nondisjunction during meiosis.
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 PAR: pseudoautosomal regions -- these region synapse and recombine with X chromosome in meiosis- SRY: sex-determining region
- MSY: male-specific region of the Y; non recombining region of the Y
- euchromatin region: functional genes
- heterochromatin region: nonfunctioning genes
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SRY features and deviations
- 6-8 weeks become active in XY embryos
- testis-determining factor (TDF) a protein encoded by the SRY gene that initiates testes formation
- deviations from normal sex determination: males w/ XX and no Y --> SRY attached to X
- females with XandY are missing SRY gene
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sex ratio
primary vs secondary
- primary sex ratios - males to females conceived in a population
- secondary sex ratio - proportion of each sex that is born
- more males born that females
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dosage compensation
balances the dose of X chromosome gene expression in females and males
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Barr bodies
- highly condensed inactive X chromosomes
- arise from the random inactivation of either the maternal or paternal chromosome
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regardless of how many X chromosomes a somatic cell possesses, all but one of them are inactivated.
how many Barr bodies in Turner's, Klinefelters or 47, XXX?
- N-1 rule, N=#of chromosomes...
- no Barr bodies in Turner's (XO)
- 1 Barr body in Klinefelter's (XXY)
- 2 Barr bodies in 47, XXX
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Lyon hypothesis
Inactivation of X chromosome is random
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The process whereby expression of genes on one homolog but not the other
imprinting
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how is sex determined in Drosophila?
male?
female?
ratio thresholds...
- Ratio of X chromosomes to the haploid sets os autosomes (A).
- Normal female: AA and XX 1:1
- Normal male: AA and XY 1:2
- up to 0.5 = male
- over 0.5 but under 1.0 =intersex
- 1.0 and over = female
- 1.5 = metafemale
- 0.33 = metamale
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