genetics ch 5 exam 2

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genetics ch 5 exam 2
2015-10-17 17:28:22
genetics exam
genetics ch 5 exam 2
genetics ch 5 exam 2
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  1. 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)
  2. 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
  3. 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
  4. 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
  5. 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
  6. sex chromosome syndromes occur due to ___________ during _________.
    sex chromosome syndromes occur due to nondisjunction during meiosis.
    • 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
  7. 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
  8. 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
  9. dosage compensation
    balances the dose of X chromosome gene expression in females and males
  10. Barr bodies
    • highly condensed inactive X chromosomes
    • arise from the random inactivation of either the maternal or paternal chromosome
  11. 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
  12. Lyon hypothesis
    Inactivation of X chromosome is random
  13. The process whereby expression of genes on one homolog but not the other
  14. how is sex determined in Drosophila?
    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