11_Linkage_disequilibrium.pdf - FRSC-BIOL 3700 11 – Linkage disequilibrium Aaron Shafer Last Lecture ● Mutation-selection[0.50(1-10-9 = 0.50-1x10-9

11_Linkage_disequilibrium.pdf - FRSC-BIOL 3700 11 –...

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FRSC-BIOL 3700 11 – Linkage disequilibrium Aaron Shafer
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Last Lecture Mutation-selection Genetic load [0.50(1-10 -9 ) = 0.50] [-1x10 -9 x 0.50= 5 x 10 -10 ] Many loci
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Last Lecture Genetic load 10 loci at w = 0.999 -> W = 0.990 100 loci at w = 0.999 -> W = 0.90 1000 loci at w = 0.999 -> W = 0.37 10000 loci at w = 0.999 -> W = 0.000045
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Last Lecture Heterozgyous effect
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Linkage and recombination Linkage disequilibrium (LD) is used to describe the associations of alleles on chromosomes Some physically linked genes (i.e. same chromosome) segregate independently; this occurs through recombination The simplest model capable of showing the effects of recombination is of a diploid species with two linked loci, each with two segregating alleles
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Linkage and recombination The probability that a recombinant gamete is produced at meiosis is denoted by r, which is often called the recombination rate Generic gamete
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Linkage and recombination There are four gametes in the population, A 1 B 1 , A 1 B 2 , A 2 B 1 , and A 2 B 2 with frequencies x 1 , x 2 , x 3 , and x 4 , respectively. Population
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Linkage and recombination The frequency of the A 1 allele, is a function of the gamete frequencies, is p 1 = x 1 + x 2 0.25 0.25 0.50 +
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Linkage and recombination The frequency of the B 1 allele, is a function of the gamete frequencies, is p 2 = x 1 + x 3 0.25 0.25 0.50 +
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Linkage and recombination Recombination changes the frequencies of these gametes in a very simple way; for example, the frequency of the A 1 B 1 gamete after a round of random mating, is x 1 : x 1 = (1 - r ) x 1 + r p 1 p 2 This is really the probability of choosing A 1 B 1 gamete from the population Gametes have one of two histories: 1) recombinant with probability r ; or 2) non- recombinant with probability 1- r
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Linkage and recombination Again, the frequency of the A 1 allele, is a function of the gamete frequencies: p 1 = x 1 + x 2 0.25 0.25 0.50 +
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Breaking this down The probability that the chosen gamete is an unrecombined A 1 B 1 gamete is: (1— r ) x 1 A recombinant gamete with A 1 B 1 is the frequency of A 1 times B 1 times the probability of a recombinant R
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