The Y chromosome that lost the male-determining function behaves as an X chromosome in the medaka fish, Oryzias latipes.
The medaka, Oryzias latipes, has an XX/XY sex-determination system, and a Y-linked DM-domain gene, DMY, is the sex-determining gene in this species. Since DMY appears to have arisen from a duplicated copy of the autosomal DMRT1 gene approximately 10 million years ago, the medaka Y chromosome is considered to be one of the youngest male-determining chromosomes in vertebrates. In the screening process of sex-reversal mutants from wild populations, we found a population that contained a number of XY females. PCR, direct sequencing, and RT-PCR analyses revealed two different null DMY mutations in this population. One mutation caused loss of expression during the sex-determining period, while the other comprised a large deletion in putative functional domains. YY females with the mutant-type DMY genes on their Y chromosomes were fully fertile, indicating that the X and Y chromosomes were functionally the same except for the male-determining function. In addition, we investigated the frequencies of the sex chromosome types in this population over four successive generations. The Y chromosomes bearing the mutant-type DMY genes were detected every year with no significant differences in their frequencies. These results demonstrate that aberrant Y chromosomes behaving as X chromosomes have been maintained in this population.
Otake
Hiroyuki
H
Graduate School of Science and Technology, Niigata University, Ikarashi, Niigata 950-2181, Japan.
Hayashi
Yusuke
Y
Hamaguchi
Satoshi
S
Sakaizumi
Mitsuru
M
D000818:Animals; D005260:Female; D029941:Fish Proteins / Q000235:genetics / Q000378:metabolism; D008297:Male; D009154:Mutation; D009990:Oryzias / Q000235:genetics* / Q000378:metabolism; D019849:Sex Determination Processes; D014960:X Chromosome / Q000378:metabolism*; D014998:Y Chromosome / Q000378:metabolism*
D029941:Fish Proteins