Local and Seasonal Variations of Lethal Frequencies in Natural Populations of Drosophila melanogaster

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Abstract
Frequencies of the second chromosome bearing lethal gene (or genes) in natural populations were examined in 5 stations, in summer and autumn seasons and in successive years in Hiroshima prefecture. The combined frequencies of lethal and semilethal chromosomes varies with the stations, seasons or years from 2.2 to 20.7%. The allelic rates within a population ranged from 0 to 60%, from the results was estimated the narrowest territory of breeding unit. The frequency of lethal chromosomes was revealed to be increased by 2.53% and that of semilethal ones by 0.99% from summer to autumn, and about 7 generations may elapse in natural populations during the period. The allelic rate was observed to be decreased by 2.26% during the 2 seasons. In spite of such accumulation of lethal genes or decrease of allelic rate in the breeding season, any remarkable changes in the frequency or rate were not observed in the same season of successive years. It was suggested that the seasonal changes in lethal frequency and the allelic rate seem to be repeated from year to year with the same fluctuation.