Once upon a time, it seemed quite simple, biologically anyway, to make a human male. All that was needed were 23 pairs of chromosomes with one of the pairs being X and Y. That compared to a female, with one of its pairs being both Xs. Recently, scientists found that there may be more to making a male than just the presence of a Y.
As a refresher since it might have been a while since some of us have had an in-depth version of the birds-and-bees talk, here is a, well, some sort of quickie. In a biologically distinguished moment, not necessarily inhabited by rhyme or reason, man and woman make a most primal exchange. For his part, man releases sperm cells. Each sperm bears either an X or a Y but only one sperm is needed to awaken an egg (always an X) that a female, for her part, releases normally every month. A man makes sperms cells anew throughout his lifetime but a woman has a fixed number of egg cells when she is born and she just releases each one every month upon ovulation. If the sperm and egg meet successfully, then an embryo is formed. Unless you hitched a ride on a comet to get here, each of us is a direct result of that process.
From that process, we get nature’s first gift pack – one set of chromosomes containing DNA from each of our parents which they inherited from theirs and so on and so forth. It is the combination which makes you unique, plus the “errors” nature makes (mutations) when it makes copies of DNA.
The Y chromosome itself has been characterized as quite impoverished by geneticist Steve Jones in his book “Y, The Descent of Men” (2003). And you will understand why when you know that the Y chromosome has only about 90 genes or so compared to the X’s over a thousand. But in this seeming genetic poverty, one gene in it reigns with radical, transformative powers – the SRY gene.
Located at the tip the Y chromosome’s short arm, the SRY gene, discovered in 1990, causes a domino activation of all other genes required to direct themselves to make the biological male. This gene is called the SRY which stands for the sex-determining region of the Y. This gene gives the instructions to make the SRY protein that nudges other sections of your DNA to gear up for biological maleness.
The SRY occupies a tiny location in the Y chromosome. But it is so potent that when it was first injected to fertilized XX mouse egg, the mouse developed as a male complete with the biological deliverables. Some medical conditions are proof of the powers of the SRY gene. One is Swyer syndrome where even if you were an XY, if your SRY gene somehow has a mutation that makes a mute SRY protein, which will make you develop as a female by default.
Another is “XX, 46 testicular disorder of sex development” whereby if you were an XX but the SRY gene somehow finds its way to your X chromosome, you will then develop male characteristics. There are also conditions where you may be an XY but if your SRY is somehow impaired, you may develop genitalia that are ambiguous.
Recently, scientists from the University in Queensland in Australia, in collaboration with some Japanese scientists, have found that even if the SRY had the determination of the sexually indomitable Genghis Khan, it will not be able to unleash its raging male-making powers until another protein unzips it. And because it is scientists and not marketing people who named the enzyme, they named it “Jmjd1a”, which for all we know may be a sexy name to geneticists. Its job is to disentangle the SRY gene before the latter could unleash its male-making powers. The scientists discovered this with mice just like they did when they discovered the SRY. They knocked off Jmjd1a in XY mice and indeed, the mice developed female characteristics.
Like the many things that could happen to the SRY gene, many things could also affect this enzyme that may help explain the sex conditions that cross the biological duality that we treat as the norm for our species. Now, male-making is unravelling to be a team effort, just like most things in life – biological or otherwise. The basic recipe for maleness (not necessarily manhood, of course) now includes: a Y chromosome, the SRY gene, and now the Jmjd1a.
I think it is quite revelatory and even redemptive that science has discovered that there is more to being male than luck merely having a “Y” drop by to make for a luck-y male. Looking at the men in my family and in my circle of friends, all of whom I love dearly, I would not have thought that something so wonderfully complicated is behind such relatively simple, predictable organisms. So hug the men in your life. I myself will but of course, only after I stop chuckling.
Maria Isabel Garcia is a science writer. She has written two books, “Science Solitaire” and “Twenty One Grams of Spirit and Seven Ounces of Desire”. Her column appears every Friday and you can reach her at sciencesolitaire@gmail.com
(Abstract model of man of DNA molecule from Shutterstock)
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