The Chromosome Complement of the Howler Monkey (Alouatta caraya, HUMBOLDT 1812)

The chromosome complement of the howler monkey (Alouatta caraya) has been studied in blood cultures cultivated in vitro for four days. The chromosome number is 52. The Y chromosome is acrocentric and ranks 19 in decreasing order of size. The X chromosome is submetacentric and ranks seventh in the same order. The autosomes, 4–14 µm long in metaphase, with arm ratios from 1.2 to 8.8, are arranged and numbered in order of decreasing size. Chromosomes 12, 18, 20, 22 and 24 are satellited, pairs 18 and 20 being the first metacentric satellited chromosomes to be described as a regular feature in higher animals.Chromosomes 21 and 22, and occasionally 23, carry a deep secondary constriction in the proximal third of the long arm. An idiogram of the haploíd chromosome set is presented incorporating measurements of 35 analyzed nuclei.