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MSU ZOL 445 - Inbreeding Handout

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Reading: Text 236 to 247Inbreeding: HandoutII. Effects of inbreedingA. Reduced heterozygosityGen 1Total = 375Total = 437.5Table 6.4Zoology 445 Fall 2006Reading: Text 236 to 247Inbreeding: HandoutI. Introduction.In many species mating is not random, and the most common deviation from random mating is inbreeding.Inbreeding = mating among genetic relatives.Measuring inbreeding. F = inbreeding coefficient = probability that two alleles in an individual are identical by descent.Calculating F from a pedigree (Fig 6.27): Either situation can occur. If the grandchild is either homozygous triangle or homozygous diamond, then she has alleles that are identical by descent. Thus, the overall probability of receiving alleles that identical by descent is:F = probability of a happening + probability that b happens = 1/16 + 1/16 = 2/16 = 1/8AM Jarosz 1Zol 445 JaroszII. Effects of inbreedingA. Reduced HeterozygosityB. Inbreeding depressionA. Reduced heterozygosityGenotype A1A1 A1A2 A2A2 Total population sizeNumber of individuals: Gen 0250 500 2501000Gen 1250 125 Total = 375 250250125Total = 375 1000Gen 2375 62.5Total = 437.5 12537562.5Total = 437.5 1000Note that allele frequency does not change,Table 6.4Measuring the inbreeding coefficient from a population sample F = H0 – HF H0Where:H0 = Expected heterozygosity if the population is randomly mating = 2pq = H0 of the text formula page 241. Note: H0 = Hs for a subpopulation in the FST formula. HF = Observed heterozygosity in the inbred population.2Zol 445 JaroszWhen F = 0.00 there is no inbreeding in the population since H0 = HF.When F = 1.00 the population is completely inbred & HF = 0.Figure 24 HartlExample: Wild oats (Avena fatua) have a mating system that allows both selfing and outcrossing.Jain and Marshall measured the amount of inbreeding in a population by determining the genotypes at two loci: (Fig 9.6 FUT)B. Inbreeding depression.Examples:Figure 6.233Zol 445 JaroszAnother example: Waterleaf a biennial (germinates and grows one year, and floweringin year two.Human example:Fig 6.28 4Zol 445 JaroszII. Population size and inbreedingA. Realize that inbreeding and genetic drift are related.Remember our earlier example:By generation 11 this population is inbreeding even if individuals in the population are choosing mates randomly.B. Rescuing small populations from the effects of small population size and inbreeding depression.Fig 9.12 FUT\Evolution Zol 445\2006\ Inbreeding


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