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The wood lemming (''Myopus schisticolor'') is a species of rodents in the family Cricetidae. It belongs to the Arvicolinae subfamily of rodents, so is a relative of the voles, lemmings, and muskrats. It is found in the taiga biome of China, Finland, Mongolia, Norway, Russia, and Sweden.〔Musser, G. G. and Carleton, M. D. (2005). "Superfamily Muroidea". pp. 894–1531 in ''Mammal Species of the World a Taxonomic and Geographic Reference''. D. E. Wilson and D. M. Reeder (eds.) Johns Hopkins University Press, Baltimore〕 ==Sex determination== Wood lemmings produce about three times as many female as male offspring. This is due to an unusual genetic system where they have two different types of X chromosomes, the normal X and a mutated X *. Females with that mutation on their X *-chromosome inhibit the male determining effect of the Y chromosome. This leads to three genetic types of females: XX, X *X and X *Y and one genetic type of males XY. The X *Y females are fertile, but only produce X * ova, which means they only produce female offspring. It is not fully known the extent to which nature balances out the differences in the adult population, but sampling studies seem to suggest males do make up as little as 25% of the population at equilibrium. Females with abnormal genotype (XO, XXY, X *YY) occur regularly. The high female sex ratio may be an adaptation against local mate competition and inbreeding during population low points.〔Gippoliti, S. (2002). (Myopus schisticolor ). 2006 IUCN Red List of Threatened Species. Downloaded on 9 July 2007〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Wood lemming」の詳細全文を読む スポンサード リンク
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