Abstract
The dominant mutant “Retarded growth” (symbol Rg) was found as a gamma-ray induced phenomenon. It is characterized by a departure from the normal type representing distinctly delayed larval growth. The homozygote is completely lethal in embryonic stage.
Linkage test showed the Rg locus to be in the third chromosome at 24.9. Further crosses with the recessive gene sm(N) gave without exception pseudo-dominantly manifested sm(N) character in Rg females. While the crosses with allelic sm(S) gave sm(S) character in only a part of Rg females, which is explained as due to a position effect. It is concluded from these results that Rg is not a gene mutation but a deletion of intercalary chromosomal segment. The left break is at 24.9 and the right break is just left by the sm(S) locus at 41.8. The deficit is about 17 units of the length of the third chromosome.
