sex linkage.txt

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Author:
rincrocci
ID:
114838
Filename:
sex linkage.txt
Updated:
2011-11-06 12:11:57
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genetics
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Description:
sex linkage
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  1. sex chromosomes
    based on cytological appearance
  2. homomorphic sex chrom
    chromosomes that look like any other (not cytologically different), but differ in major sex determination of genes
  3. heteromorphic sex chrom
    one of the homologues carrying the major sex determination gene ecomes degenerate or cytologically different
  4. sex chrom systems
    • x/y system: humans, mammals, dogs, cats, some plants (ie cannabis, female is xx, male is xy)
    • Z/W system: birds and butterflies, and wild strawberries (ie zz is male, zw is female)
  5. homogametic sex
    • in x/y: humans xx is female
    • in z/w: birds zz is male
    • (homozygous)
  6. heterogametic sex
    • x/y: human xy is male
    • z/w: bird zw is female
    • (hemizygous)
  7. sex limited
    • expressed in ONE sex or the other, but gene can be combined anywhere in the genome
    • ie milk production gene
  8. sex influenced
    • heterozygotes express one phenotype in one sex and another in the other sex
    • ie baldness (male pattern)
    • BB - baldness in female and male
    • Bb - baldness in MALE, NOT females
    • bb - no baldness
  9. X-linked gene examples
    • Red-Green colorblindness: in 4-8% males
    • Hemophilia: bleeding
    • Lesch-Nyham syndrome: movement problems, self mutilation
    • Duchenne muscular dystrophy: muscular degeneration
  10. X-linked Sex limited examples
    testicular feminization: recessive on X insensitive to testosterone - XY ind develop as FEMALES (gene on x does NOT produce testosterone)
  11. Y-linked
    • Has to come from males
    • ie: hairy ears
  12. SEX LINKAGE in PEDIGREE analysis
    • X-linked DOMINANCE
    • X-linked RECESSIVE
    • Y-linked Inheritance
  13. X-linked DOMINANCE
    • XA Xa
    • Affected males pass on trait to ALL daughters, but NO sons (sons get Y)
    • Affected females pass on traits to HALF of sons and HALF of daughters
  14. X-linked RECESSIVE
    • Many more MALES vs females show the trait
    • OFFspring of affected males will NOT be affected (all DAUGHTERS will be carriers and ALL sons will be affected)
    • Sons of affected males do NOT inherit X from father so NOT affected OR NOT a carrier
  15. Y-linked Inheritance
    ONLY affected in males, NOT females
  16. Aneuploidy
    • Addition or Subtraction of chromosome relative to their normal number
    • Ie downsyndrome: chrom 21 ADDED
  17. Euploid
    • Normal # of chromosomes characteristic of a species or exact multiples of that #
    • ie fruit: if increase in Ploidy level, fruit Increases in size
  18. Monosomic
    • Aneuploids caused by NON-disjunction (failure of separation of chromosomes or chromatids
    • (2n-1)
    • one member OF a pair of homologues is missing (ie 22 on one pair, and 23 on another pair, so total chrom for human of monosomic 18 (chrom 18 missing) is 45 (as opposed to 46))
  19. Trisomics
    • Aneuploids caused by NON-disjunction (failure of separation of chromosomes or chromatids
    • (2n +1)
    • EXTRA copy of a chromosome is present
  20. Non-Disjunction diagram
    DRAW it
  21. Downs Syndrome
    • characterized by mental retardation, eye folds, shorter lifespan
    • Maternal age: as females increase in age, increase chances of Downs (as eggs stay in body longer, increase in mutation)
  22. Facts on birth defects
    • 1/180 live births have some aneuploid condition
    • 15% of pregnancies spontaneously abort - many aneuploidy
  23. Turner Syndrome
    • XO
    • survivable condition
  24. Kleinfelters
    • XXY
    • Males: mostly detected if have problems conceiving children (reduced fertility)
  25. Supermles
    • XYY
    • Taller than average
    • CAN produce normal offspring
  26. Amniocentesis (AFT) & chorionic villus sampling
    Withdraw fluid, centrifuged & cell culture for biochem & chromosomal studies
  27. Types of Chromosomes (based on appearance)
    • Holocentric: entire chromosome acts as centromere
    • Metacentric: Centromere is in the center (how we normally draw chromosomes…looks like this - X)
    • Telocentric: centromere is at the END (on the bottom), NOT in humans
    • Aerocentric: centromere is at the beginning (on the top)
  28. Linkage
    genes residing in the SAME chromosome pair
  29. cis/trans
    • if both RECESSIVE mutations on the same member of chromosome pair, they are COUPLING (CIS)
    • A----B / a----b
    • If recessive mutations on DIFFERENT chrom pairs, they are TRANS
    • A----b / a----B
    • CLOSER Genes are, the LESS recombination occurs
  30. Facts of recombination
    • Freq. of recombinants b/w 2 genes is a fxn of physical distribution b/w them (ie - closer genes, LESS recombination occurs)
    • Recombination as measured by markers is RECIPROCAL (ie - both products of exchanging occur w/equal freq)
    • Recombination occurs @ PROPHASE I of meiosis, when homologues are synapsed together & may continue into metaphase
    • Any one recomb. occurs b/w 2 of the 4 chromatids, ONE from each homologue, but NEVER b/w sister chromatids (always occurs b/w two different X's)
    • ie X X, these 4 chromosomes can recombine, but not the first two with each other, only the first with one of the last two)
    • 2 of the 4 chromatids will be recombinant and 2 will be parental
    • occurs at different places in different meiocytes
  31. Coefficient of coincidence (COC)
    • OBSERVED crossover / EXPECTED crossover =
    • ie - observed crossover is the addition of both amount of crossovers
    • expected crossover is the multiplication of crossover occurrences b/w both regions and these percentages multiplied by the total (ie .16 x .48 x 879[total offspring])
  32. Interference RATE
    • 1 - COC = .6 ie
    • so 60% interference

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