| Popis: |
The wood lemming is unique in the following respects: (1) the sex ratio is unequal, the frequency of males is 0.20–0.30; (2) two types of females occur, type MF producing progeny of both sexes, type F producing daughters only; and (3) two sex chromosome types of females exist, XX and XY. The hypothesis presented accounts for these and other known facts concerning sex ratio, reproduction biology and chromosome constitution. It is suggested that an X-linked mutant gene affects the male-determining action of the Y, thus converting some XY animals into females. These females normally produce one kind of eggs only; by a mechanism of selective non-disjunction in the foetal ovary only X-carrying eggs are formed. Thus, XY females are of type F, XX of type MF. |
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