XX/"XO" sex determination system in a population of Peruvian owl monkey, Aotus.

The chromosome complement of a group of owl monkeys with typical pelagic features characteristic of Aotus inhabiting the upper Amazonian region in South America was analyzed by various band techniques. A diploid chromosome number of 2n = 52 is reconfirmed in the females. A Y-autosome translocation resulting in a complement of 2n = 51 in the males constitutes a unique XX/"XO" sex chromosome system in this population. Karotypic comparison of this Peruvian Aotus (2n - 52 female/51 male) with the Bolivian Aotus (2n = 50 female/49 male) shows the existence of a large degree of analogy of chromosome banding. However, complicated inter- and intra-karyotypic differences between the two chromosome races can be depicted, and substantiates our postulation that the owl monkey is an evolutionary actively diverging species.