Genetical Studies on the Effects of X-Rays in the Silkworm Bombyx mori L. I. Differential frequency of chromosomal fragmentation by X-ray treatment in F₁ hybrids of different female parents

抄録

F₁ larvae of different strains, i.e., Cambodge, Okusa, C122 Benyo, N1, C4, Taiwan No. 8, and Mus-1, used as female parents and crossed to p^sY males, were treated with 4000r on the first day of hatching to study the maternal effect on the frequency of p^s- carrying chromosome fragment elimination. The results have been presented in Tables 1, 2, 3, and 4, and Figs. 1, 2, and 3.
Various hybrids used in the present investigation have given statistically highly signficiant difference in the frequency of chromosome fragment, carrying p^s gene, elimination. The strongest maternal effect was shown by Benyo strain, a trimoltine Chinese race, thus suggesting that the eggs of this strain transmit some such biochemical substances which render Benyo×p^sY hybrids extremely radio-resistant.
There was also highly remarkable inter-varietal difference in the average size of the spot which shows that the actual time of the fragment elimination is influenced by the type of maternal parent.
Size and number of spots do not seem to be correlated and can hence be thought to be controlled by different mechanisms.
It is concluded to emphasize that various female parents afford different opportunities to p^s-carrying chromosome fragment for entering into chromosomal rearrangements (healing and/or restitution).