Y chromosome different from mitochondrial DNA
The Transcaucasian mole vole, Ellobius lutescens, the Zaisan mole vole, Ellobius tancrei, and the Japanese spinous country rats Tokudaia osimensis and Tokudaia tokunoshimensis, have lost the Y chromosome and SRY entirely. Tokudaia spp. have relocated some other genes ancestrally present on the Y chromosome to the X chromosome. Both sexes of Tokudaia spp. and Ellobius lutescens have an XO genotype (Turner syndrome), whereas all Ellobius tancrei possess an XX genotype. The new sex-determining system(s) for these rodents remains unclear.
The wood lemming Myopus schisticolor, the Arctic lemming, Dicrostonyx torquatus, and multiple species in the grass mouse genus Akodon have evolved fertile females who possess the genotype generally coding for males, XY, in addition to the ancestral XX female, through a variety of modifications to the X and Y chromosomes.
In the creeping vole, Microtus oregoni, the females, with just one X chromosome each, produce X gametes only, and the males, XY, produce Y gametes, or gametes devoid of any sex chromosome, through nondisjunction.Outside of the rodents, the black muntjac, Muntiacus crinifrons, evolved new X and Y chromosomes through fusions of the ancestral sex chromosomes and autosomes.Modern data cast doubt on this hypothesis. This conclusion was reached by scientists who studied the Y chromosomes of rhesus monkeys. When genomically comparing the Y chromosome of rhesus monkeys and humans, scientists found very few differences, given that humans and rhesus monkeys diverged 30 million years ago.Some organisms have lost the Y chromosome. For example, most species of Nematodes. However, in order for the complete elimination of Y to occur, it was necessary to develop an alternative way of determining sex (for example, by determining sex by the ratio of the X chromosome to autosomes), and any genes necessary for male function had to be moved to other chromosomes. In the meantime, modern data demonstrate the complex mechanisms of Y chromosome evolution and the fact that the disappearance of the Y chromosome is not guaranteed.
not same as not identical to distinct from separate from unlike