MALE-BIASED DISTRIBUTION OF THE HUMAN Y-CHROMOSOME GENES SRY AND ZFY IN THE LIZARD CALOTES-VERSICOLOR, WHICH LACKS SEX-CHROMOSOMES AND TEMPERATURE-DEPENDENT SEX DETERMINATION

In the present investigation on the lizard Calotes versicolor, which l acks temperature-dependent sex determination, all the conventional cyt ological techniques used failed to resolve a distinguishable pair of s ex chromosomes. However, probing of the genome with the human Y-linked genes SRY and ZFY showed sex-specific bias in their distribution. Whi le the SRY probe hybridized to all the males, more than half of the fe males examined did not show any hybridization. ZFY hybridized to both the sexes, giving two bands; one was common to all the individuals of both sexes, but the other, of the lower molecular length, occurred in all the males but in less than 50% of females. This predominantly male -specific band is named AMF. The SRY-positive females were also positi ve for the AMF of ZFY. As positive as well as negative females were fe rtile and none of the males lacked SRY, it appears that SRY is essenti al for males only and that both the genes are syntenic in this species . This report raises interesting possibilities on the differentiation of the sex chromosomes in C. versicolor and evolution of SRY/ZFY on th e Y chromosome of eutherian mammals through the ancestral group(s) tha t harbour sex-independent SRY- and ZFY-related genes.