The human Y chromosome is threatening to disappear. It is not the number of copies of the Y chromosome that is in any immediate danger: there is still one copy of the Y chromosome in almost each cell in the male body, or about 30 trillion copies of it in each man. But, the size of the Y chromosome – and I don’t know how else to break the news to you – is shrinking.

To put things in order, I would like to remind you that there are 23 pairs of chromosomes in our body. They contain our DNA – the instruction-manual to everything that is going on in our body, from the color of our eyes to how fast our heart beats. One of the 23 pairs are our sex-chromosomes. Women have two X chromosomes. Men have one X chromosome and one Y chromosome (I will simply call it Y, pronounced ‘why’, as in ‘why not?’).

Scientists believe that the shrinking of Y began 300,000 years ago when two regular-looking chromosomes decided to specialize. Throughout this period, the X chromosome has preserved 98 percent of its genetic content. The manly Y, on the other hand, has grown a beard and gone rogue, retaining only three percent of its ancestral genes. And so, if you look closely at the X and Y chromosomes, you will be struck by the difference: the X chromosome looks like all other non-sex chromosomes – two plump hotdogs twisted around each other at the middle, taking the shape of the letter ‘X’. On the other hand, Y doesn’t look like the letter “Y” (its name derives from the order in which it was discovered as in X, Y, Z; not from its shape). Instead, it looks diminished and humbled by a tragic history of loss – a piece of paper crumpled into a little ball. It seems of no use, or distinction – an object of no desire.

Some women would take comfort in the demise of Y. They might see Y as the source of all trouble, a collection of genes that add no value to the world, that propagate undesired manly traits such as selective hearing (“they never listen”), selective memory (“he didn’t remember my birthday”), addiction to TV-channel flipping, over-confidence, and hairy ears. Other women, however, might miss the Y, and admit that “the sex [chromosome] was great while it lasted.”

Scientists try to remain calm. They found that from a genetic standpoint, humans are very similar to each other. Pick any two random men, and you will find that their DNA is 99.9 percent identical. The same applied to two randomly selected women. If you compare women to men, however, the picture changes dramatically: the DNA of women and men is only 98.5 percent identical. This 1.5 percent difference may still seem small, until you consider that the DNA of a human and a chimpanzee is also 98.5 percent identical. In other words: from a genetic standpoint, my wife’s DNA is as close to my DNA as it is to the DNA of a chimpanzee. And please, I beg, don’t jump to conclusions.

What does this difference between the genetic composition of men and women mean? It is obvious that the genes on Y encode for male-specific characteristics: they determine the sex of the fetus, the formation of testes, and the formation of sperm cells. What is less obvious is this: first, the Y genes are present in almost all somatic cells; and second, these genes affect the development of organs outside of the genital system.

In an article in the Journal of Proteome Research, for example, Anna Meyfour and her colleagues described 48 Y-chromosome genes. Most of these genes are related to male-specific characteristics, but some genes have a role in the development of tooth enamel, the kidneys, the heart, even the brain.

For those of us who thought that the differences between men and women stem from different hormonal environments, these findings are a dramatic twist in the plot.

Doctors and scientists have long known that a sea of difference exists between men and women in their tendencies to suffer from different diseases. Four times more men than women are diagnosed with autism-spectrum-disorder. On the other hand, women are more likely to suffer from auto-immune diseases. These differences may be due to a different hormonal environments, differences in behaviors (men engage more in risky behaviors), but some of the differences may be due to the expression of Y-chromosome genes.

According to some scientists, the shrinking Y is expected to completely disappear in exactly 4.6 million years. It leaves ample time to answer questions like: can better understanding of the Y chromosome and its genes help cure diseases that present differently in men and women? How will a world without Y look like? How are men really different from women? And why is Y disappearing?

Dr. Shahar Madjar is a urologist working at Aspirus Keweenaw Hospital. He sees patients in Laurium, Houghton and L’Anse. Contact him at smadjar@yahoo.com.