Unique multiple sex chromosomes of the tree mouse Vandeleuria o. oleracea: identification of X₁ and X₂

Abstract

The tree mouse Vandeleuria o. oleracea has an odd diploid chromosome complement (2n=29♀/♂) accompanied by a unique multiple sex-chromosome mechanism (X₁X₂Y♂/X₁X₁X₂♀). In the present paper the sex chromosomes have been identified unequivocally with the help of G-banding and DNA replication patterns which confirm our earlier suggestion that the X₁ is smaller in size than the simple mammalian X, and also that the combined sizes of the X₁ and X₂ (3.8 and 1.7 per cent respectively) approximate to the size of the conservative mammalian X (5 per cent). It is proposed that the mammalian X has attained a minimum functional size so that further reduction is not tolerated.