Figure 3.11 (a) Allelic states (or allele frequencies) for 107 D. melanogaster populations where 16 individuals (eight of each sex) were randomly chosen to start each new generation. Initially, all 107 populations had equal numbers of the wild-type and bw75 alleles (the latter causes homozygotes to have a red-orange and heterozygotes an orange body color so genotypes can be determined visually). The allelic states of the population rapidly spread out and many populations reached fixation or loss by the nineteenth generation. (b) The expected frequency of populations in each allelic state determined with a Markov chain model for a population size of 16 with 107 populations that initially have equal frequencies of two alleles. The experimental D. melanogaster populations show a higher rate of fixation and loss than the model populations, suggesting that the population size was actually less than 16 individuals each generation. The D. melanogaster data come from Table 13 in Buri (1956).

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