A CHIASMATE SEX QUADRIVALENT IN THE MALE OF AN ALTICID BEETLE, CYRSYLUS VOLKAMERIAE (F.)

Abstract

A Puerto Rican fleabeetle, Cyrsylus volkameriae (F.), has the karyotype 13^II + X₁X₂y₁y₂ (♀): 13^II + X₁X₁X₂X₂ (♂). One exceptionally large autosomal pair and all sex chromosomes are totally heterochromatic or almost so. The sex quadrivalent of the male is the only functional chiasmate sex quadrivalent known. It has probably been formed by two reciprocal translocations between a largely or totally heterochromatic autosome and both neo-X and neo-Y. Except for the sex-determining genes, few or no major genes are considered to be located on the sex chromosomes.