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 incompatibility between second chromosomes and their genetic backgrounds, where a decrease in the average viability of heterozygotes in the foreign 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). This feature is different from that of the incompatibility found in the Ishigakijima 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 dysgenesis, as strong P-transposase activity was shown in this population with the GD sterility test. Although a property similar to that of the Osaka population had been detected in the Katsunuma population, an increased frequency of the lethal-carrying chromosomes had been found in the foreign genetic background relative to the native one, and was not seen in the Osaka population.