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Where the Crossovers are: Recombination distributions in mammals

Where the Crossovers are: Recombination distributions in mammals. 경원. Overview. Nonrandom recombination events: most recombination events occure at highly localized hot spot. Characterize the frequency and spatial distribution of meiotic recombination events.

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Where the Crossovers are: Recombination distributions in mammals

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  1. Where the Crossovers are:Recombination distributions in mammals 경원

  2. Overview Nonrandom recombination events: most recombination events occure at highly localized hot spot. Characterize the frequency and spatial distribution of meiotic recombination events. The classic tools; difficult in detecting low frequency events.

  3. Crossover distributions in mammals – an historical perspective • Genetic versus physical distances: centimorgans per megabase pair • Cytological studies: observing CHIASMATA or detecting of chromosome-associated protein complex involved in recombination. • Pedigree and linkage disequilibrium (LD) analysis: pedigree approaches guided by LD analysis

  4. Characterizing mammalian hot spots • Development of SNP sequencing: inclease marker density • Sperm DNA – allows many meiotic products, detect very low-frequency recombination. • 약 0.5 kb 정도의 resolution을 가지는 hot spot location을 detecting • 결점은 male에서만 사용가능 하다는 것이다.

  5. Measure of LD • Definition: A measure of whether alleles at two loci coexist in a population in a nonrandom fashion. • Strong LD 는 두 loci 사이에 재조합이 거의 일어나지 않는 것을 의미한다. • Dij= xij-piqj • D’=Dij/Dmax (D’=1; complete LD,D’=0; free association)

  6. D’ example • SNP1: C 와 G의 빈도가 각각 0.90, 0.10 • SNP2: A와 T의 빈도가 각각 0.55, 0.45 • 4가지 가능한 조합 (CA, CT, GA, GT) • 기대되는 haplotype (0.495, 0.405, 0.055, 0.045) • 관찰된 haplotype (0.450, 0.450, 0.100, 0) • LD 값은 D는 각각 -0.045, 0.045, 0.045, -0.045) • D’은 -1 ~ 1 • 여기서 절대값으로 구한 D’이 일반화된 LD 값이된다. • LD 값이 1이면 완벽한 LD 임을 나타내고, LD값이 0이면 LD가 없음을 나타낸다.

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