Sex isn’t as simple as male or female.

It’s not just about chromosomes. Or genitals. Or reproductive cells. Or any other binary metric. (Binary refers to something that can only take one of two, either/or states.)

People have a huge range of genetic, environmental and developmental variations. These can produce in the same person a mix of what are thought of as masculine and feminine traits. When it comes to sex, millions of people don’t fit a narrow, binary definition. That’s through no fault of their own — and many don’t even know it. Instead, scientists say, sex should be viewed in all its complex glory.

For instance, in Turner syndrome, women lack one X chromosome. They do have a uterus, but no ovaries. So they can’t make gametes. If sex were defined by which gamete you make, Biason-Lauber wonders, what sex would someone with Turner syndrome be? And this condition is not all that rare, she adds. Some 1 in every 2,000 to 2,500 female babies are born with it. Many won’t find out until adulthood. Others may never be diagnosed.

About 1 in every 650 male babies are born with two or more X chromosomes and one Y. This is called Klinefelter syndrome. Many men with this won’t learn they have an extra chromosome unless they go for fertility treatments, Biason-Lauber says. These people have testes and penises. They don’t, however, make sperm. So a definition based on gametes would leave these people out.

One gene on the Y chromosome is called SRY. It is important for male sex development, but not essential. Sometimes, SRY jumps out of the Y chromosome when chromosomes are divided up before sperm production. It can attach itself to an X or some other chromosome. If the hitchhiking SRY gene is passed on, it may result in people who have two X chromosomes plus a stray SRY gene. These people will develop as males. But lacking a full Y chromosome, they won’t make sperm.

Some people have an X and a Y chromosome but carry a version of SRY — or changes in other genes — that doesn’t spur typical male development. These people develop as females but don’t make eggs.

Other people with an X and a Y may have versions of some genes that prevent their bodies from responding to testosterone and other male sex hormones. Those people have testes inside their abdomens. But the rest of their bodies develop as female.

• https://www.snexplores.org/article/human-sex-complex-biology-male-female

• Science Proves There are More than Two Human Sexes

• https://www.dw.com/en/even-the-science-agrees-there-are-more-than-two-genders/a-57062033