| From the above - mentioned chromosome associations, the gametes with 21-
and 22 chromosomes may be produced in heterozygotes, besides a small number
of 20- and 23 chromosome gametes, but the last ones may not fertilize actually
by their weakness of viability due to extreme overdose of chromosomes. In heterozygotes, if the female gametes with 21-, 22- and 20 chromosomes are produced in the ratio of 10 : 8 : 1 and the male gametes with 21-, 22- and 20 chromosomes fertilize in the ratio 20 : 4 : 1 by competition among them as was shown in the results of normals x heterozygotes and its reciprocal cross and in that of observations of pollen tetrads of heterozygotes, zygotes with 42- (normal), 43- (heterozygote), 44- (homozygote), 41- (het. lax - eared) and 40 chromosomes (homo. lax - eared) may arise in the ratio 1 : 0.94 : 0.15 : 0.15 : 0.005 respectively. This calculated ratio seems to be very near to the actually observed ratio 1 : 0.93 : 0.14 : 0.14 except lax - eared homozygotes. Theoretically expected lax - eared homozygotes with 40 chromosomes did not arise actually. Perhaps these zygotes might have aborted on the way of their development. Through the cytogenetic results of dense - eared mutants the author assumes that dense - eared mutants arise by partial or whole duplication of a peculiar chromosome (non IX) bearing the dense - eared promoting (or lax - eared suppressing) gene and that lax - eared mutants arise by partial or whole deficiency of the same chromosome. The locus of the dense - eared promoting gene is in one segment of the long arm of this chromosome. This peculiar chromosome perhaps corresponds either to 5B (V) or 5D (XVIII) chromosome, which is homeologous with 5A (IX) chromosome of Chinese - Spring wheat, or to 4D (XV) chromosome having lax - eared suppressing gene. |
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