"Mice can be male without Y chromosome"

"Reproductive biologist Monika Ward of the University of Hawaii in Honolulu and colleagues started with mice that have only one X chromosome (and no second sex chromosome). Normally those animals would develop as females. But when the researchers manipulated genes found on the X and another chromosome, the mice became males that could produce immature sperm. Those engineered males fathered offspring with reproductive assistance from the researchers, who injected the immature sperm into eggs, Ward and colleagues report in the Jan. 29 Science...

ActivatingSox9 in a genetically female embryo will cause it to develop as a male, Ward and colleagues found. But those males didn’t make sperm. “The testes were empty,” says Ward.

In order to produce sperm, mice need the Eif2s3y gene, the researchers had previously discovered. In the new experiment, the mice were missing the gene because they didn’t have Y chromosomes. So researchers substituted a similar gene from the X chromosome calledEif2s3x. Only one copy of the Y version is needed to make immature, tailless sperm, but it takes at least five copies of the X version to do the same thing. “This indicates that the Y chromosome gene is the strong one,” says Ward.

Her research suggests that the Y chromosome has optimized production from genes that are necessary for making males...

Primates, including humans, don’t have Eif2s3y genes on their Y chromosomes. No one yet knows whetherEif2s3y’s function in primates was taken over by other genes on the Y, its X counterpart or genes elsewhere in the genome."

https://www.sciencenews.org/article/mice-can-be-male-without-y-chromosome