Oh Why Our Y? 


Pity the mice. On countless occasions, mice without any say in the matter stand in for humans. And what we do to them can be perverse or bizarre—done just so we can understand us a bit better.

Or not.

So now male mice have been “conceived” in the laboratory who only possess two genes—from the whole Y chromosome.

And that Y chromosome works. Better, the two gene males can still father—with a little help from their human laboratory handlers performing some relatively inexpensive in-vitro fertilization.

Their kids? Pretty normal looking mice.

So is the Y chromosome all that it’s cracked up to be? Is it really necessary?

That depends. 

The Human Y

Cancer researchers are fond of saying “we can cure most cancers—in the mouse.”

The human Y chromosome is, to use an infelicitious phrase, a different kettle of fish.

Mice have 14 genes on their Y chromosomes. Humans have 23 genes. And the big kahuna—at least as far as fertilization is concerned—is a gene called SRY.

No, SRY is not a stock symbol or yet another internet marketing company. SRY is a gene that makes for human maleness—and aids the embryo to develop.

You can ask any XX male.

Yes, that is correct—there are normal human males out there who lack a Y chromosome. What they do have is the SRY gene, attached to an X chromosome.

For it turns out humans have relatively small parts of their X and Y chromosomes that exchange genetic material somewhat  readily. Which is how you get a healthy, normal looking XX human male. Who can also produce male offspring like himself.

But there are other uses to the Y chromosome, besides hairy ear lobes and creating males.

The Majestic Moment of Mom

As you would expect, the womb is a very important place. How you treat Mom has a lot of impact on her kids.

Particularly mice. A recent study out of McGill (see the Economist, December 14, 2013) took female mice and kept them folate deficient during conception. Then their male offspring were kept folate deficient, too.

This was not good news for the males. First, they were far less capable of having offspring. Next, their own offspring were deformed.

A full 27% of the folate deficient produced visibly weird looking kids. Only 3% of the normally fed males produced obviously deformed children.

Was this a genetic change? No, not because the genes were different—but because some genes were turned on, others off. 

The folate deficient males had a whole bunch of genes that were newly methylated—one of the main issues today of epigenetics—how gene expression is controlled. And some of the genes that were turned on or off by folate deficiency are heavily involved in diseases like cancer and diabetes.

The environment of the mother has much to say about the development of the child—and to what kind of male or female they turn out to be.

The Nature of Sex

Sex is not what it’s cracked up to be.

For a long time people thought that if you have a Y chromosome you’re male, and if you have two Xs you’re female.

Not so.

There are plenty of XY females out there, just as there are XX males. The “maleness” genes may not be part of the Y chromosome. For what really matters is how genes are expressed.

This has confused people for a long time. People are even more confused by “obviously” male or female folk who tell you they are the opposite; by males and females who act as if they were the opposite sex but continue to think themselves as males and females; and by people who seem to be both male and female.

These "confusions" become easier to comprehend if people see genes—and biology in general —as different forms of information .

Physicists are now quite used to the idea. The universe is not mass and energy, quarks and larks—it’s a vast, endless field of information.

So is the human body - and every human being. And the set of signals that make us who we are is constantly changed by the environment we live in.

Instead, we like to think about things that are “permanent”—like genes. If genes change they change very slowly.

So we’re taught. But what really matters more is how those genes are used. 

Some will be turned off before birth by epigenetic processes not yet understood. Some will be turned on by the 100,000 chemicals added to the environment since World War II, again in ways not presently understood.

And much will be shifted by culture and politics and economics—all particularly human ways of carrying information. So that a child born in a particular Venezuelan village may be raised as a female until 12, then treated and trained as a male thereafter, especially if born with a micropenis.

Sex is both complicated and immensely changeable, because everything we do is changeable.

Even the nature of the Y chromosome.

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