FERTILE XO MALES AND FEMALES IN THE VARYING LEMMING, DICROSTONYX-TORQUATUS PALL (1779) - UNIQUE GENETIC SYSTEM OF SEX DETERMINATION

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 they^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. © 1979 The Genetical Society of Great Britain.