How the Ryukyu Spiny Rat Lost its Y Chromosome

Male and female Ryukyu spiny rats have only X chromosomes.
Male and female Ryukyu spiny rats have only X chromosomes.

Usually if a mammal doesn't have a Y chromosome in its cell then a male can't be produced; however, the Ryukyu spiny rat doesn't need a Y chromosome to get born. Using gene cloning and mapping technologies

Associate Prof. Asato Kuroiwa of the Faculty of Science and her team investigated how this is possible and also solved the mystery of what happened to three genes on the Y chromosome.

The researchers found that among these three genes, the one essential for sperm production was missing and the other two survived by relocating to the X chromosome. In mammals this type of gene expression is usually limited to males, but they also discovered that female Ryukyu spiny rats have this remarkable ability.

Despite lack of a Y chromosome and missing the gene related to important male functions, male Ryukyu spiny rats are born and manage to produce sperm. This suggests that new genes are acquired in males, and that the species is maintained despite the missing Y chromosome. These findings beget new areas of exploration into the evolution of the Y chromosome, and yield subjects for future studies include locating and analyzing the new genes acquired by the male Ryukyu spiny rat.

The results of this study were reported in Chromosoma: Biology of the Nucleus on May 5, 2010.

Contact information:
Associate Prof. Asato Kuroiwa
Faculty of Science, Hokkaido University

See also: Y chromosome losing all genes, but men won't become extinct