Hello, and welcome back to Everyday Science.<\/p>\n
Quick question: what is small, weird, and yet has been central to the lives of half the human race?<\/p>\n
The answer \u2013 if you didn\u2019t guess from the picture, above \u2013 is the Y chromosome. This is part of human DNA<\/a> that makes foetuses male.<\/p>\n New FeatureIn ShortQuick Stories. Same trusted journalism.<\/p>\n Along with a role in sperm production, this was once seen as more or less the only function of the Y chromosome.<\/p>\n And yet recent research has found its story is more interesting than we thought. It has turned out to be surprisingly common for men\u2019s cells to lose their Y chromosomes as they get older.<\/p>\n This phenomenon seems to raise the risk of a host of medical conditions, including heart attacks, cancer and Alzheimer\u2019s disease. The latest research suggests that in a way, it may even hasten the ageing<\/a> process itself.<\/p>\n Weird genetic garbage<\/p>\n The explanation for many of the Y\u2019s weird features lies in how sex is determined, so first we need a bit of background biology.<\/p>\n DNA, present in nearly every cell in our body, is packaged into discrete bundles, called chromosomes. Humans have 23 pairs of chromosomes, with one inherited from their mum and the other from their dad.<\/p>\n Most of these chromosomes are very similar, but not one pair, the sex chromosomes; women carry two X chromosomes, while men carry one X and one Y.<\/p>\n The X is nearly three times the size of the Y chromosome, but the Y carries one very important gene; it is activated in seven-week-old embryos to kick off testicle formation.<\/p>\n It is because the X and Y, alone among the chromosomes, are different to each other, that there are several peculiarities about the Y.<\/p>\n When DNA is duplicated before cell division, if mistakes arise, they can usually be eliminated in something like a copy-checking process, where one chromosome is compared to its partner.<\/p>\n But because the Y is different to the X, it cannot be checked in this way, and so genetic mistakes have crept in during evolution.<\/p>\n This is why the Y is full of genes with mutations that make them defunct and why it is among the smallest of our chromosomes, with many mutated genes having been jettisonned in the past.<\/p>\n Scientists describe the Y as \u201cgenetic garbage\u201d. Some have even predicted that over millions of years, it might dwindle to nothing, leading to the end of men.<\/p>\n Goodbye Y<\/p>\n In the present day, geneticists have noticed the Y chromosome may be absent from some of a man\u2019s cells, especially in older men, with up to two in five men having detectable Y loss by age 70.<\/p>\n Usually a cell dies if it loses a chromosome, but it was thought that because the Y\u2019s main job is sex determination in the womb this phenomenon had no impact on adults.<\/p>\n That changed in 2014, when Swedish scientists showed that Y loss in blood cells correlates with how long men live<\/a> \u2013 those who have Y loss in some of their cells die five years sooner. Many further studies showed Y loss raises the risk of heart attacks or diseases such as cancer and Alzheimer\u2019s.<\/p>\n Correlation or causation?<\/p>\n The problem with studies like these is they are a kind known as \u201cobservational\u201d, which means scientists just observe patterns of disease incidence and some risk factor \u2013 in this case Y loss.<\/p>\n Y loss could just be an innocent bystander, a marker of ageing, a bit like grey hair, but not be directly causing the health problems, said Professor John Perry, a geneticist at the University of Cambridge. \u201cI\u2019m always skeptical of any form of observational [study],\u201d he said.<\/p>\n The bystander theory was strengthened by Professor Perry\u2019s 2019 research<\/a> that found men are more likely to have Y loss if they have certain genes<\/a> (carried by other, non-sex-determining, chromosomes) that make someone\u2019s DNA copying machinery more prone to errors. Those genes could both lead to Y loss in immune cells, and separately lead to heart disease, cancer, and so on.<\/p>\n \u201cThe theory is Y loss is just the manifestation of a whole lot of problems happening all over the place,\u201d said Professor Perry. His work even showed that those same genes were linked with breast cancer in women \u2013 an effect that definitely couldn\u2019t be happening through the Y chromosome, because it\u2019s absent in women.<\/p>\n Theory of ageing<\/p>\n But since then, two other kinds of research have suggested this is wrong, and Y loss really is harmful after all. One was the creation of mice whose immune systems were replaced with cells lacking the Y chromosome<\/a>, which developed heart disease. \u201cThis indicates its not just a bystander,\u201d said Dr Lars Forsberg, a geneticist at Uppsala University in Sweden, who was involved in the work.<\/p>\n The other sheds light on why Y loss could be involved in so many conditions. It concerns a theory that says most diseases of ageing arise because of the growing accumulation in our bodies of \u201csenescent cells<\/a>\u201d, which have become damaged and are malfunctioning.<\/p>\n Senescent cells are supposed to be killed off by our immune system. But in mice, immune cells that lack a Y chromosome are less able to do this, Dr Forsberg helped to show in August<\/a>. \u201cIt showed how loss of Y can be associated with disease in so many different organs,\u201d he said. \u201cThe immune system is not doing its proper job to remove senescent cells.\u201d<\/p>\n Professor Perry said the work in mice was elegant, but it didn\u2019t show that Y loss was directly harmful for every disease it has been linked with by observational studies. \u201cDifferent hypotheses could be true for different diseases,\u201d he said.<\/p>\n Reason for men\u2019s shorter lives<\/p>\n Men tend to be intrigued by Y chromosome research, but that may be due to misunderstandings, said Professor Perry. \u201cPeople think about loss of Y chromosome in their body, and they think that that might influence masculinity<\/a> in some way. But this is about the function of [immune] cells.\u201d<\/p>\n There are blood tests that can tell you if you have Y loss but there is no point for most men, and the only thing you can do to cut your risk of Y loss is follow health advice, like avoiding smoking and eating healthily.<\/p>\n Men may now have even more reason to do so, however. Dr Forsberg has calculated from UK data that Y loss explains half of the difference in lifespan between men and women, with women living to 83 on average, and men 79. He presented preliminary results at the European Society for Human Genetics conference this year.<\/p>\n If all else fails, scientists in the fields of ageing and longevity are getting increasingly interested in senescent cells, and are developing drugs to clear them from the body. If senescent cells really are behind the impact of Y loss, then one day, the treatment be as simple as a daily pill.<\/p>\n I\u2019ve also written<\/p>\n![\"Older](\"https:\/\/www.newsbeep.com\/ca\/wp-content\/uploads\/2025\/10\/SEI_270439766-e1760620997790.jpg\")
The Y chromosome may explain why some men seem to age better than others (Photo: Getty)<\/p>\n