A NEW EXTRA-CRESCENT GENE (E^Dl) CAUSING DEGENERATION OF ABDOMINAL LEGS IN THE SILKWORM

Abstract

In this paper, the author described manifestation and genetical behavior of an extra-crescent gene discovered from a commercial race of silkworm, and discussed about its genetical relationship with E pseudo-alleles on the 6th chromosome.
1. Homozygotes for this character have a pair of extra-crescent markings on the 6th segment, no star-spots on the 8th segment, and no abdominal legs at the 6th segment (Fig. 1). In heterozygotes, manifestation of the extra markings on the 6th segment is incomplete and variable as shown in Fig. 2. The penetrance and manifestation of E^Dl gene are affected by some genetical constitution of strains.
2. This mutant reveals no abnormalities of sexual organs and has no lethal effects on the embryo.
3. No abdominal legs on the 6th segment is complete recessive to normal and the extra-crescent markings on the same segment are incompletely dominant. Both the characters, however, are controlled by a single gene.
4. This gene is located in the E pseudo-allelic region on the 6th chromosome, and symbolized as E^Dl: extra-crescent and degenerated abdominal legs.
5. The recombination value obtained between E^Dl and E^H genes was 0.32±0.09%.
6. E^Dl +/+ E^N individuals have no abdominal legs on the 6th segment. This fact seems to show that the locus of E^Dl falls partly on the site of E^N. And taking the results of ltikawa (1952 b, 1957), Tsujita (1955) and Tsujita et al. (1959 b) into consideration, it is assumed that the arrangement of genes at the E region is as follows: E^H E^N E^Dl E^Ca E^Kp E^Nc E^Cd.