What Makes a Male

Just how much of the Y chromosome is needed to make a male?

Not much, according to a new study!

We've known for just a couple of decades that only one gene determines gender. Now we also know that it takes just two genes out of the 78 genes on the Y chromosome to actually produce a healthy male... well, for now, male mice.

Still, this has huge implications for humans and infertility in males. It could mean that men with immature sperm can reproduce through in vitro fertilization. In the study, researchers tried exactly that with mice.

They injected immature mouse sperm into mouse eggs. This immature sperm contained two genes from the Y chromosome - the SRY gene, which determines sex, and the Eif2s3y, which produces sperm cell precursors.

In 9% of the cases, the offspring produced grew into normal, healthy male mice that were infertile but could reproduce with help.

Even thought that's well below the 26% success rate when they injected eggs with a Y chromosome, it's still eye-opening.

To try this on humans, scientists would need to tweak the method, since Eif2s3y is not on the Y chromosome. Instead, there's a copy on the X chromosome.

It's possible that by using Eif2s3y, researchers can one day develop precursor sperm cells that mature enough to produce viable offspring. These male children would also have immature sperm cells and would need help reproducing.

This study doesn't render the rest of the Y chromosome useless, though. In fact, those genes are necessary to produce fully viable sperm capable of fertilization.