Manhood may have received its nastiest blow yet. Biology textbooks have long informed us that the ‘Y ‘chromosome, present only in males, is critical for reproduction. But a study by researchers at the University of Hawaii (UoH) has shown that healthy mice can be made, using assisted reproduction techniques, without any of the all-important ‘Y’ chromosome genes. Normally a person gets 23 chromosomes —the repository of our DNA — from each parent; 22 of the pairs are called autosomes and the ‘X’ and ‘Y’ are called sex chromosomes. The ‘Y’ chromosome is present in males, who have one ‘X’ and one ‘Y’ chromosome, while females have two ‘X’ chromosomes.
The diminution of man started two years ago after the research team, led by Monika A. Ward, UoH, showed that of the many genes of the ‘Y’ chromosome, only two — ‘Sry’ and ‘Eif2s3y’ — were needed for male mice to sire offspring with assisted fertilisation. Now, the same team, with a collaborating researcher from France, Michael Mitchell [French National Institute of Health and Medical Research] (INSERM, Marseille), upped that and produced males completely devoid of the entire ‘Y’ chromosome.
In last Friday’s edition of the journal Science , Ms. Ward and her colleagues describe the production of these gender-bending mice by detailing how they first replaced the first gene ‘Sry’ with one from the autosome and the other with a gene from the ‘X’ chromosome. While one may quibble that the ‘X’ chromosome used was from the male, there’s been related research showing that the days of the ‘Y’ chromosome are numbered. Both the ‘X’ and ‘Y’ chromosomes are known to lose genes over time and due to the frenetic shuffling of evolution. However, women — by virtue of having two ‘X’s — were somehow able to swap and maintain their genes among themselves. The ‘Y’ — unpaired and solitary in the male — does not get a chance to replenish its genes as much. Also, there are far fewer genes on the ‘Y’ chromosome than on the ‘X’. Jennifer Graves at the Australian National University caused consternation earlier this decade when she estimated that within five million years, the ‘Y’ chromosome, and the men it produces, would disappear. More ominous was genetics professor Bryan Sykes who predicted the demise of the ‘Y’ chromosome, and of men, in as little as 1,00,000 years in his 2003 book Adam’s Curse: A Future without Men .
Not so grave A flurry of studies that have since looked at the proclamations of Prof. Sykes and Prof. Graves more closely have now found that the future isn’t as dire. The loss of genes, apparently, isn’t a steady loss and there are long periods of stability followed by bursts of attrition.
Jennifer Hughes and her colleagues at the Whitehead Institute in Cambridge, Massachusetts, compared the human ‘Y’ chromosome with that of the ‘Y’ from the chimpanzee — supposed to have diverged atleast 4 million years ago from the line that begat humans — and also with that of the rhesus monkey which diverged from humans 25 million years ago. They reported in the journal Nature in 2012 that human chromosomes had lost no further genes in the last six million years, and only one in the last 25 million years. “The ‘Y’ is not going anywhere and gene loss has probably come to a halt,” Dr. Hughes told the BBC.
While masculinity can breathe easy, Dr. Ward’s studies may provide new lines of investigation for male infertility. Though these results only hold for mice and there are formidable ethical barriers to be negotiated, one thing is incontrovertible by now: it simply isn’t raining men anymore.
jacob.koshy@thehindu.co.in
