It turns out that males aren’t on a path to extinction as previously thought. A study entitled “Strict evolutionary conservation followed rapid gene loss on human and rhesus Y chromosomes” has contradicted the longstanding belief that the Y chromosome is dying out. The study, authored by Jennifer F. Hughes et al, was published in February 2012 and was reported by Jessica Hamzelou in Issue 2853 of New Scientist.
It is widely known that the X and Y chromosomes are what make men and women different. Each female egg contains an X chromosome, and male sperm are equally divided between containing X and Y chromosomes. As such, in reproduction, a fertilised egg will contain one X chromosome from the egg and either an X or Y chromosome from the sperm, resulting in an XX (female) or XY (male) combination of chromosomes (Reece et al. 2011, 294).
Research conducted by Graves (2004) and others concluded that over 300 million years, the number of genes on the Y chromosome has reduced by 1393! The X chromosome, however, have barely lost any. Genes transmit hereditary information; the most significant gene in the Y chromosome being the gender determining SRY gene (Sinclair et al. 1990). Graves (2004) predicts that within ten million years, all of the Y chromosome’s remaining genes will be extinct.
So it’s clear that the extinction of the Y chromosome would also mean the extinction of men. This highlights the importance of the recent breakthrough to predicting the long-term future of humanity.
Jennifer Hughes’ research has uncovered an important development in the rate of genetic change in the Y chromosome. The X and Y chromosomes “evolved from an ordinary pair of autosomes during the past 200-300 million years” (Hughes et al. 2012). As a result of this common ancestry, the genes would cross between the almost identical X and Y chromosomes (Hamzelou 2012). However, approximately 166 million years ago one of five significant “stratification” (Hughes et al. 2012) events occurred that inhibited X-Y gene exchange over a chromosome fragment. This event significantly altered the structure of the Y chromosome (Hamzelou 2012).
The final stratification event occurred 30 million years ago, providing a checkpoint in time that could be used for Y chromosome gene comparison. Five million years after this final event, the human and Old World monkey lineages separated (Hughes et al. 2012). Hughes sequenced the Y chromosome of an Old World primate (Rhesus macaque) in order to identify the genetic changes between the primate and humans over twenty five million years. Twenty genes were found in the primate’s Y chromosome that matched genes in its X chromosome, humans sharing nineteen of these genes (Hamzelou 2012).
Thus the Y chromosome has actually only lost one gene since the final stratification event, and in fact, gene numbers in the Y chromosome are holding steady (Hamzelou 2012). This breakthrough has lain to rest the misconception that the male species is destined for extinction, and has uncovered important information about human chromosomal development.
List of References