Cytogenetics of Howler Monkeys

Abstract

Cytogenetic analysis of howler monkeys have exhibit diploid numbers ranging from2N=44 in Alouatta seniculus to 2N=58 in A. pigra with several interspecificchromosomal rearrangements such as translocations and inversions. Other remarkablegenetic features are the multiple sex chromosome systems and the presence ofmicrochromosomes. Multiple sexual systems are originated by Y-autosometranslocations, resulting in the formation of trivalents X1X2Y in males of A. belzebuland A. palliata, and quadrivalents X1X2Y1Y2/X1X1X2X2 in males of A. seniculus, A.pigra, A. macconnelli and A. caraya. Fluorescent in situ hybridization (FISH) analysesin the South American species have revealed that segments with homeology to humanchromosomes #3 and #15 (synteny 3/15) are involved in these sexual systems. Differentauthors agree with the assumption that these diverse sex chromosome systems share thesame autosomal pair and the rearrangement may have occurred once. Recentcytogenetic characterization of A. pigra and A. palliata, have shown that the autosomesinvolved in the translocation that formed the sex chromosome systems in theMesoamerican and South American species are different. Two independent events of Yautosometranslocations might have led to different sexual systems. Together with themultiple autosomal rearrangements found in the genus, the howlers`sex chromosomesystems constitute an illustrative example of the possible chromosomal evolutionmechanisims in Platyrrhini.