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Figure 2.13 The impact of various systems of consanguineous mating or inbreeding on heterozygosity, the fixation index (F), and the inbreeding coefficient (f) over time. Initially, the population has allele frequencies of p = q = 0.5 and all individuals are assumed randomly mated. Since inbreeding does not change allele frequencies, expected heterozygosity (He) remains 0.5 for all 20 generations. As inbreeding progresses, observed heterozygosity declines and the fixation index and inbreeding coefficient increase. Selfing is 100% self-fertilization whereas mixed mating is 50% of the population selfing and 50% randomly mating. Full sib is brother-sister or parent-offspring mating. Backcross is one individual mated to its progeny, then to its grand progeny, then to its great-grand progeny and so on, a mating scheme that is difficult to carry on for many generations. Change in the coefficient of inbreeding over time is based on the following recursion equations: selfing ft+1 = 1/2(1 - Ft); mixed ft+1 = 1/2(1 - Ft)(s) where s is the selfing rate; full sib ft+2 = :/4(1 + 2ft+1 + ft); backcross ft+1 = :/4(1 + 2ft) (see Falconer & MacKay 1996 for detailed derivations).

ancestors and shows only the paths where alleles could be inherited in the progeny from individual A.

To begin the process of determining the autozygos-ity for G, it is necessary to determine the probability that A transmitted the same allele to individuals B

and C, or in notation P(a = a'). With two alleles designated 1 and 2, there are only four possible patterns of allelic transmission from A to B and C, shown in Fig. 2.15. In only half of these cases do B and C inherit an identical allele from A, so P(a = a') = V2.

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