Abstract
By irradiation of X-rays, several mutants with respect to the second chromosome of Bombyx mori had been obtained. One of them, “Sable, ” has so far been studied genetically. It appeared as a single individual in the F1 of the X-rayed PsY females (that is striped-marked and yellow blooded) crossed with untreated Py males (that is normal-marked and white blooded). The mutant shows very dirty body color and is expressed by the symbol “Sa”.
The typical “Sable” shows normal eye-spots and trace of the crescent and the star-spots. This characteristic behaves epistatic to the plain, equistatic to the normal and the moricaud, and hypostatic to the striped marking. Although Sa belongs to the P multiple allelic group, the crossing over value between Sa and Y is only 1.8 per cent, much lower than that (25.6 per cent) for P and Y.
Besides the visible characteristic, it accompanies lethal action. The lethal action of “Sable” is manifested, when homozygous, in the later embryonal stage.
When SaY was crossed with Py, PSaY individuals were obtained. Among the offspring of PSaY males, mated to py females, PSaY individuals reappeared which lost lethal action.
Lethal action of Sa seems to depend upon a chromosomal deficiency and attachment of Py to SaY or non-disjunction of the two chromosomes would have compensated the deficient part of SaY chromosome. Moreover, the presence of chromosomal inversion has been proved genetically.
