Y Chromosome Vanishes in Some Older Males
The loss is linked with several health conditions and shorter lifespans
Hiya!
It’s well known that, on average, females have longer lifespans than males. This is true not just for our species, but for most or all mammals. Some research even suggests that females have “always” outlived males, even during severe epidemics and famines, and continue to do so in every country worldwide today.
Of course, several theories have been proposed to explain this phenomenon, such as hormonal differences, males tending to be higher risk takers, smoking habits, and females’ extra X chromosome. I recently wrote about how researchers discovered that the bonus, supposedly inactive, female X chromosome becomes active with age in mice and may provide all sorts of benefits, including extending longevity.
Recently, however, researchers have proposed that the X chromosome is not the only sex chromosome involved in the male-female lifespan discrepancy; the Y chromosome is likely also involved. I fell down quite the rabbit hole while investigating it, but this latest research suggests that males lose this chromosome from many of their cells as they age, making them more susceptible to age-related diseases and early deaths.
Chromosomes
Before discussing the research, it’ll be helpful to refresh our knowledge about chromosomes and their functions. Chromosomes are threadlike structures that transport genetic information, DNA, from cell to cell, ensuring its accurate copying and distribution during cellular division.
Most humans have 46 total chromosomes, which come in 23 pairs, with half of each pair inherited from one parent and the remaining half from the other parent.
Of these pairs, 22 are collectively called autosomes, while individual pairs are identified by numbers between 1 and 22 based on their size, with Pair 1 being the largest and Pair 22 being the smallest. Autosomes contain genes that influence everything from our predisposition to diseases to our physical traits.
Meanwhile, the 23rd pair is our sex chromosomes, identified by the letters X and Y, instead of numbers. This pairing is distinct from our autosomes because they are directly responsible for determining our biological sex. (To be clear, our sex chromosomes do not define our gender identity, which is a social construct.)
Generally speaking, females have a pair of X chromosomes (XX) while males have an X and a Y (XY). However, dozens of other combinations of the X and Y sex chromosomes naturally exist, too, including X, XXX, XXY, XXYY, and more. People with these sex chromosomes are known as intersex, an umbrella term to categorize anyone with sex chromosomes that differ from the XX-XY binary.
It’s important to note that people with intersex traits have always existed, as intersex is entirely normal and not a disorder, disease, or condition. An estimated 1 in 100 people, or about 2 percent of the global human population, have intersex traits.
Anyway, this article is about the Y chromosome, which is most well-known for determining the sex of a fetus and maintaining sperm production. However, much about it remains a mystery.
Mystery of the Y
One reason the Y chromosome is mysterious is that, of the two types of sex chromosomes, most research thus far has focused on the X chromosome, since all known people — female, male, and intersex alike — have at least one. (The human egg only supplies an X chromosome, while the sperm can provide either an X or a Y chromosome.)
But that’s not the only reason.
As Jenny Graves, a geneticist and professor at the La Trobe Institute for Molecular Science, explained to Alex Hughes of BBC Science Focus,
"In comparison to the X, the Y is tiny. There are only 45 genes on the Y chromosome, and it is just one of these that makes you male. A few others help make sperm, but for the others, we don't quite know why they are there. We just can't really get rid of them. That's compared to between 900 and 1400 in the X."
I should note that while researching this article, I found varying claims regarding the precise number of genes on the Y chromosome. In 1998, it was believed that the Y chromosome contained over 200 genes. In 2011, it was estimated to have over 700 genes. More recently, in 2023, the number drastically fell to 27 genes, before increasing slightly in 2025, to between 50 and 60 genes.
The Y chromosome's size and mysterious features make it challenging to analyze, which is part of why it was the last human chromosome to be fully sequenced in 2023 (and is also likely why the gene number estimations dropped so significantly around that time).
While mysteries remain, after sequencing, scientists now know that the human Y chromosome has undergone some significant changes throughout human evolution.
For instance, once upon a time, the Y chromosome had at least as many genes as the X chromosome, but has slowly shed most of them over the last 166 million years. Today, the Y chromosome is only about a third of the size of the X chromosome.
As evolutionary geneticist Jenny Graves wrote in The Conversation, gene sequencing the Y chromosome revealed that these days,
“The Y has a lot of DNA sequences that don’t seem to contribute to traits. This ‘junk DNA’ is comprised of highly repetitive sequences that derive from bits and pieces of old viruses, dead genes and very simple runs of a few bases repeated over and over.”
The unstable design, combined with the fact that it’s been losing about five genes every one million years, puts the Y chromosome at risk of disappearing in an estimated 11 million years.
That said, some scientists believe it may not disappear entirely but instead disperse and relocate to different chromosomes, a phenomenon that has already been observed. Experts also believe that a new sex chromosome will likely evolve to take its place, potentially resulting in a new type of human.
While such possibilities are a long, long way off, there is another, similar yet very different, and more immediate thing happening to the Y chromosome affecting males today.
The Vanishing Y Chromosome
In a phenomenon entirely separate from the human species potentially losing the Y chromosome permanently over the next few million years, individual males can permanently lose their Y chromosome in some of their cells as they age.