REVISED KARYOTYPE OF ALOUATTA-CARAYA (PRIMATES, PLATYRRHINI) BASED ONSYNAPTONEMAL COMPLEX AND BANDING ANALYSES

Most primates studied have the usual XX/XY sex-chromosome system. Howe ver, exceptions to this rule among howler monkeys have been suggested by several authors. Recently a quadrivalent was discovered in male mei osis of Alouatta caraya and it was established that this species has a n X1X2Y1Y2 sex chromosome system. On that basis, a cytogenetic analysi s of 25 males of this species is described, showing the corrected kary otype of this species. Each chromosome involved in the particular sex- chromosome system of this species is identified on the basis of mitoti c chromosome measurements, G and C-banding patterns as well as on the relative measurements of synaptonemal complexes. It is now established that A. caraya has a karyotype with 2n = 52 in both sexes, and that t he male one shows a single autosome #7 (X-2) besides the X (X-1) and t he two products of the reciprocal translocation between the second aut osome #7 and the Y chromosome (Y-1, and Y-2), while females show a hom omorphic pair #7 (X-2) and a pair of X-1. The evolutionary implication s of the exceptional primate species having composite sex-chromosome s ystems are discussed.