Hokkaido University : How the Ryukyu Spiny Rat Lost its Y Chromosome

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.
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.
Interesting, isn't it ?