Sex Determination of the « Pseudo-XO/XX » Type in the Brazilian Lizard Polychrus Sp. (Sauria, Iguanidae)

SUMMARY

The karyotype of the Brazilian lizard Polychrus sp showed 2n=20 chromosomes for the female and 2n=19 chromosomes for the male. The meiotic cells of the male in diakinesis and metaphase I showed 8 bivalents and 1 trivalent. In metaphase II there were cells with n=9 chromosomes, and cells with n = 10 chromosomes. The sex determining mechanism was interpreted as belonging to the « pseudo XO/XX » type, which differs from the X₁X₂Y/X₁X₁X₂X₂ type because the Y is morphologically indistinguishable from the X₂ chromosome. This is the second occurrence of this case to be described in the vertebrates.