Evolution of W, female-specific sex chromosome through the comparative genomics between Bombyx mori and B. mandarina

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We analyzed the W-chromosome construction in B. mori, B. mandarina and other related species. B. mandarina and B. huttoni was branched 14 million years ago(MYA). In B. mandarina one copy set of two genes was translocated from an autosome to W-chromosome(z1-z20) in 7 MYA, and z1-z20 was duplicated on W-chromosome 0.3 MYA. Such a new type of B. mandarina containing duplicated z1-z20 on W-chromosome had spread drastically. But, since Japan islands have been isolated from the continent 0.1 MYA, the new type did not invade in Japan. In present, there are 4 copies of z1-z20 in all B. mori, and B. mandarina except for Japan.