Fertile XO males and females in the varying lemming, Dicrostonyx torquatus pall. (1779)

Abstract

In the varying lemming, only some of the females exhibit a conventional sex chromosome constitution, XX. Many fertile females as well as all males have one X chromosome. The Y chromosome was not revealed by the methods employed. It has been shown that the sex of XO specimens depends on a genetic factor which displays two alternative forms. The XO lemmings possessing the m-form develop as males; those carrying the f-form develop as females. This factor is most likely X-linked. The XX females are heterozygous for this factor or homozygous for the m-form. In progeny of the XO and heterozygous XX females an excess of daughters is observed, the secondary sex ratio being 0·67 and 0·75 respectively. Two or three mutational events must have given rise to this complex system of sex determination. The possible adaptive significance of the relevant system is discussed.