Abstract
Most of the mutations discovered in Aphiochaeta sp. to date show irregular inheritance. Among these mutations, truncate (t) which appeared spontaneously from wild stock, shows various grades of truncations on wing margins between the 2nd longitudinal vein and the 4th longitudinal vein, ranging all the way from extreme truncate to normal.
When truncate is crossed with wild type, truncate does not appear ordinarily in F1 but in rare cases it appears in up to a maximum of 8%. F2 shows a penetrance of from to 20%. In brother and sister matings of truncates a few normals appear, and even after continued selections for more than 50 generations, normals were never completely eliminated.
F1 expressivity and penetrance of crosses of brother and sister truncates of high expressivity was higher than the F1 expressivity and penetrance of crosses of brother and sister truncates of low expressivity, and the F1 of intermediate type gave intermediate results.
Selection of high-expressivity-individuals resulted in producing extreme-expressivity-individuals only, and penetrance become 100%, but at the same time the accompanying decrease in reproductive powers made this line very diff cult to continue.
Selection of low-expressivity-individuals toward the plus and minus direction was effective; this suggests the existence of modifiers.
The truncates among the F1, F2 or F3 individuals of low expressivity obtained from the cross of low expressivity-individual and wild type were crossed successively with the wild of the same brood, and resulted in that the expressivity became concentrated on the selected grade, although the penetrance was variable, being high in some and low in others.
This result also suggests the presence of modifiers.
Sex does not have any bearing on the appearance of truncate character.
The chief factor for truncate is located on one of the autosomes.
