Explained | The remarkable endurance of the Y chromosome, ‘master of maleness’ Premium

Many animal species have a genuine fear of losing the Y chromosome in the distant future. This has already happened in some species that have naturally lost this chromosome. Such animals provide us with models to understand the process of sex-chromosome turnover and a means to repurpose another chromosome into a sex chromosome.

This article is part of a fortnightly column exploring contemporary concepts and issues in genetics.

The Y chromosome, often referred to as the “master of maleness”, has long captivated scientists and historians alike. In humans, in addition to the 22 pairs of chromosomes in each, we have a pair of sex chromosomes called X and Y. Sex as a specification is determined by these sex chromosomes. They carry sex-determining genes. All biological males have X and Y chromosomes and all biological females have two X chromosomes. The ‘sex-determining region Y’ on the Y chromosome determines the biological male sex. 

Estimated to have emerged around 200-300 million years ago in a common ancestor of all mammals, the Y chromosome has had a unique genetic journey, and embedded within its DNA lies a remarkable tale of evolution. Scientists published the complete genetic sequence of the Y chromosome in 2003. This sequence provided an outline of 23 million bases of the 60 million or so bases that together make up the Y chromosome. In total, the chromosome encoded for only 55 genes and accounted for around 2% of the genetic material inside a cell.

Many researchers jokingly refer to the Y chromosome as the “juvenile delinquent” among chromosomes thanks to its abundance of repetitive sequences, poor functional utility (with a small number of genes), reluctance to socialise (i.e. recombine with other chromosomes), and a high proclivity to degenerate over the course of evolution.

Indeed, because it has little potential to recombine, the diminutive Y chromosome has been passed from father to son, carrying the legacy of generations. Scientists have extensively studied it to understand human migration and evolution. It has also fuelled countless debates, unravelled the mysteries of paternity, revealed genetic diversity, and illuminated the intricate tapestry of our shared past.

In a landmark genetic study, published in March 2003 in the American Journal of Human Genetics, researchers reported that around 0.5% of all the men in the world have inherited a Y chromosome from the Mongol emperor Genghis Khan or one of his descendants. While the Y chromosome has been at the centre of many scientific and social controversies involving sex determination and gender discrimination, we would be better off not underestimating its influence on other aspects of health as well.

In fact, contrary to initial assumptions that the chromosome is degenerating and shrinking over time, and possibly has little functional role, researchers have discovered of late that the Y chromosome possesses genes that are vital to biological functions, including those linked to ageing and lifespan regulation (recent studies have shed light on an intriguing connection between the human Y chromosome and longevity).