Nagao, K., Takenaka, N., Hirai, M. and Kawamura, S. (2005). Coupling and decoupling of evolutionary mode between X- and Y-chromosomal red-green opsin genes in owl monkeys. Gene, 352:82-91.

Different evolutionary fates of Y-chromosomal red-green opsin genes of owl monkeys between northern and southern species. In northern species, the Y-linked opsin gene has been retained by concerted evolution with X-linked original copy. In southern species, Y-autosome fusion disrupted the evolutionary coupling between the Y- and X-linked opsin genes, and the Y-linked opsin gene became a pseudogene and multiplicated. X and Y represent X- and Y-linked opsin genes, respectively. Y/A indicates the red-green opsin gene on the Y-autosome fusion chromosome. N and S represent the northern and southern species groups, respectively. Arrows indicate DNA sequence exchange between the X- and Y-linked opsin genes.