S2M3 biochem

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sweetlu
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144752
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S2M3 biochem
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2012-04-08 16:09:48
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S2M3 biochem
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S2M3 biochem
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  1. X- inactivation
    • - begins at XIC (X inactivation center) at Xq13
    • - acheived by methylation initiated by XIST (X inactivation specific transcript)
    • - XIST product is an RNA
  2. SRY
    • - sex determination gene of males
    • - proximal to PAR1(obligatory crossover region of Xp and Y)
    • - unequal recombination can yeild XX males and XY females
  3. PAR
    • - pseudoautosomal regions of sex chromosome
    • - distal regions of both sides of both chromosomes
    • - recombination of sex chromosomes occurs here
    • ***genes at PAR regions of p arm of X and Y are NOT inactivated***(if they were females would show sx of turners syndrome(45,X0))
  4. Dynamic mutation
    • - mutation which changes apon transmission
    • - ie trinucleotide repeats
    • - increase in number or TNR => increased chance of passing threshold and showing phenotype(disease)
  5. Anticipation
    • - progressively earlier onset and increased severity of a disease in successive generations
    • - due to expansion of unstable triplet repeats over generations
  6. haplotype
    - groups of alleles that are in coupling(linked alleles on teh same chromosome)
  7. linkage disequilibrium
    • - bad allele is found together with a specific marker in (nearly) all people carrying the bad allele
    • - a significant deviation from mean = linkage disequilibrium
    • - low mutation and low crossover

    - haplotypes freq 0.25= equilibrium
  8. genomic imprinting
    • - differential expression of alleles based on parental origin\
    • - homologous chromosomes are not equally expressed
  9. differential expression in trophoblast and embryoblast
    - paternally derived genes are essential for trophoblast

    - maternally derived genes are essential for embryonic development
  10. heterodisomy
    - due to nondisjunction at meiosis 1
  11. DMR
    • - differentially methylated region
    • - on genes that are imprinted
    • - include ICR(imprinting control region)
    • - these areas on the gene can methylated based on which parents gene is supposed to be expressed
  12. isodisomy
    - occurs through a nindisjunction at meiosis 2
  13. 6 assumptions of Hardy-Weinburg equation
    • - No migrantion, mutation, selection or consanguity(inbreeding)
    • - random mating and large population
  14. additive gene effect
    • - affect of alleles at one locus/gene is codominant
    • - two alleles at different loci having same level of influence on a trait
    • - ie- two different allele combonations result in same height
    • (Aa,bb and aa,Bb ==> same height)
  15. polygenic trait
    - determined by more than one gene, BOT NO environmental effect
  16. regression toward the mean
    • - parents at the most extreme values, the children are often found towards the population average
    • - because the extreme values of the parents are likely due to environmental effect unlikely to be repeated in the offspring
  17. threshold traits
    • - traits that when combined can push a person past "threshold" (a certain value on a "liability" bell curve, beyond which disease is expected)
    • - once enough traits have come together to get a person past threshold, that person will have the disease
    • - before the threshold, person is unaffected
  18. incidence calculation
    • - rule of thumb risk
    • - risk of a sibling of an affected individual=
  19. characteristics of multifactorial diseases
    • - higher risk if >1 family member affected
    • - higher risk if affected person has severe sx
    • - higher risk if affected person belongs to less affected sexx
    • - risk decreases rapidly if the relationship is less close
    • - risk of first degree relative is \
  20. linkage
    • - 2 loci closely adjacent on the same chromosome and alleles are observed to be inherited together
    • - not useful for multifactoral inheritance
  21. association
    - a disease and a marker allele occur together more often than expected from the individual frequencies
  22. OCA2
    - gene with 75% of responsibility for blue vs brown eyes
  23. genetic drift
    - change in allele frequency from one gen to the next by random effects
  24. allele sharing in relatives
    • 1st- siblings and parents= 50%
    • 2hd- half sibs, uncle/niece, GP/gc= 25%
    • 3rd- first cousins= 12.5%
    • 4th- second cousin= 6.25%
  25. X inactivation facts
    • - more genes on p arm escape inactivation
    • - females express 2x more steroid sulphase than men
  26. skewed X inactivation
    • - females showing expression of a disease that is on a single X chromosome
    • - ie partial expression of DMD (if mutated X expression is greater than 50%)
  27. reciprocal translocation carriers
    • -phenotypically normal typically
    • - large risk of repro problems
    • - offspring will have unbalanced translocation
  28. x autosome translocation
    - leads to female infertility
  29. LOD score
    • - logarithm of the odds, determines if linkage exists
    • - >3= proof of linkage
    • - <-2= proof of non linkage
  30. heritability
    • - part of total variance that is caused by genes
    • - correlates to the slope of the line comparing quantatative data b/t individuals with differing amounts of shared alleles
    • - high heritability= small/no environmental effects

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