A TYPE OF INCOMPATIBILITY BETWEEN GENES AND THEIR GENETIC BACKGROUND INDUCING DECREASE IN HETEROZYGOTE VIABILITY APPROXIMATELY EQUAL TO THAT OF HOMOZYGOTES, FOUND IN A NATURAL-POPULATION OF DROSOPHILA

In the Osaka population of Drosophila melanogaster, we found an incomp atibility between second chromosomes and their genetic backgrounds, wh ere a decrease in the average viability of heterozygotes in the foreig n genetic background relative to that of the native one (A'/A = 0.889) was about equal to that in non-lethal homozygotes (C'/C = 0.874). Thi s feature is different from that of the incompatibility found in the I shigakijima population, where little difference in average viabilities of heterozygotes between the native and foreign backgrounds was found , whereas in mean non-lethal homozygotes viabilities a large decrease was seen. This feature is supposed to be induced by the P-M hybrid dys genesis, as strong P-transposase activity was shown in this population with the GD sterility test. Although a property similar to that of th e Osaka population had been detected in the Katsunuma population, an i ncreased frequency of the lethal-carrying chromosomes had been found i n the foreign genetic background relative to the native one, and was n ot seen in the Osaka population.