Evolution of a Multiple Sex-Chromosome System by Three-Sequential Translocations among Potential Sex-Chromosomes in the Taiwanese Frog Odorrana swinhoana

Translocation between sex-chromosomes and autosomes generates multiple sex-chromosome systems. It happens unexpectedly, and therefore, the evolutionary meaning is not clear. The current study shows a multiple sex chromosome system comprising three different chromosome pairs in a Taiwanese brown frog (Odorrana swinhoana). The male-specific three translocations created a system of six sex-chromosomes, male X1Y1X2Y2X3Y3-female X1X1X2X2X3X3. It is unique in that the translocations occurred among three out of the six members of potential sex-determining chromosomes, which are known to be involved in sex-chromosome turnover in frogs, and the two out of three include orthologs of the sex-determining genes in mammals, birds and fishes. This rare case suggests sex-specific, nonrandom translocations and thus provides a new viewpoint for the evolutionary meaning of the multiple sex chromosome system.

Automated summary

Translocations between sex chromosomes and autosomes can generate multiple sex chromosome systems. In a Taiwanese brown frog, a unique multiple sex chromosome system was discovered, involving three different chromosome pairs with translocations occurring among potential sex-determining chromosomes, including orthologs of sex-determining genes in various vertebrates. This rare case suggests sex-specific, nonrandom translocations, shedding light on the evolutionary significance of multiple sex chromosome systems.