The Persistence of Deleterious Genes in Natural Populations of Drosophila melanogaster

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Abstract
The second chromosomes of D, melanogaster were isolated from several Japanese natural populations by using the completely marked inversion method. The relative frequencies of chromosomes carrying lethal, semi-lethal, subvital, and normal genes were estimated. The total frequency of deleterious chromosomes in the small populations was significantly lower than that in the larger populations, and the level was maintained for at least one year without any marked change. The allelic rate of lethals isolated from the smaller populations was remarkably higher than that in the larger populations. The two lethal chromosomes carried by a small population were found to be maintained for at least one year in the same population. The effective size of the smaller populations was estimated to be about 1700 and that of the larger populations about 20000 according to Prout's formula.