It was revealed that the mutant Nd-t, which had been mapped at 0.0 position on the twenty-third linkage group, was not a gene mutation but a chromosomal aberration of the type T (23; 25) Nd. A series of crossing over experiments was carried out to revise the genetic map of the twenty-third linkage group. Heterozygous F1 males of the type BphB tub sp/Bphc ++ were backcrossed to BphB tub sp females. The recombination value between Bph and tub obtained from the segregation in male larvae was 6.88%, whereas the value between tub and sp was calculated to be 15.98% based on the observation of female moths. Taking previously determined order of gene arrangement on the chromosome into consideration, the map units of the genes on the twenty-third linkage group were revised as follows.
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