Persistence of lethal genes in Japanese natural populations of Drosophila melanogaster.

ANY lethal genes are concealed in heterozygous condition in natural popuMlations of Drosophila. The viability of lethal heterozygotes appears to be slightly (24%) inferior to that of normal heterozygotes (STERN et al. 1952; HIRAIZUMI and CROW 1960) and lethal genes should be selected out from a population sooner or later. However, some lethal genes have been maintained from generation to generation against natural selection. MUKAI and BURDICK (1959) reported that a lethal gene, which was extracted from a natural population, had been maintained in experimental populations for a long time owing to its heterotic action regarding female fecundity. The persistence of lethal genes in cage populations was also demonstrated by SPIES et d. (1963) and by YTTERBORN (1968). A long-term persistence of lethal genes in natural populations of the Ukraine, U.S.S.R., was also reported by GOLUBOVSKY and VICTOROVA (1968). This paper describes a case of persistence of lethal genes in natural populations at Kofu-Katsunuma during the past eight years. Several mechanisms of persistence will be discussed.