Wednesday, 21 March 2012

Demise of the Human 'Y' Chromosome?

The presence of a Y chromosome in the human genetic code is what makes males male. Recent concern that this gender determining chromosome is slowly but surely disappearing has been further questioned through the comparison of human and rhesus monkey genetic coding. This study has concluded that very little has changed in the last 25 million years to the structure of the human Y chromosome after it diverged from that of the rhesus macaque, giving hope to the continuation of such an integral part of life (Callaway 2012).

Figure 1: Rhesus macaque, the link between
the history and survival of the Y chromosome.
(France-Presse 2007)
Around 200-300 million years ago, the first environmentally dependent Y chromosome was present. Factors such as temperature and habitat are thought to have influenced the gender of animals at this time before genetics did such task. Through evolution in the proceeding years, a gene called SRY (sex-determining region of the Y) evolved from its relation gene SOX3. This split then created the Y chromosome (SRY) and X chromosome (SOX3) (Callaway 2012). From this point forward, the genes on the Y chromosome went through a period of mass decay, causing only 3% of the original amount to remain. This occurrence, over 30 million years ago very much contributed to the concern of the science world that the Y chromosome would once again go through such a process and ultimately fade away (Marsh et al 2012).

All of the concern for the Y chromosome’s future is based on the fact that, due to its separation from the X chromosome all those millions of years ago, it has become singular and unable to rely on a ‘partner’ chromosome to repair any mistakes made in the replication process. This is referred to as crossing over. The Y chromosomes inability to perform such a task has left it highly vulnerable to genetic decay and alteration, fuelling the concern for its distinction (Marsh et al 2012).

Recent decoding, however, of the rhesus macaque, an Old World Monkey, by geneticist Jennifer Hughes of Whitehead Institute for Biomedical Research in Cambridge, Massachusetts has surprisingly concluded that the human Y chromosome displays a loss of only one gene in the male-specific region of the Y (MSY) over the past 25 million years (Hughes 2012). This study has ultimately disproven the notion that the Y chromosome has continually decreased in gene numbers after its divergence from the rhesus.

Figure 2: Human X & Y Chromosomes
(Trafton, 2010)
 All of these new found elements of the history of the Y chromosome have given hope and reassurance to the existence of the sex determining chromosome for millions of years to come. Also, through the decoding of the Y chromosome of the rhesus, only the third Y ever to be fully decoded, enables another comparative tool for further studies into the history of genetic processes and the evolution of such.

In conclusion, the existence and stability of the Y chromosome has been deemed to continue for millions of years to come through the comparative analysis of the Y chromosome of humans and last common ancestor the rhesus macaque. This advance has settled the concern that this sex determining and ultimate key to reproduction in humans is set to diminish and disappear. 

Reference List:

Callaway, E 2012, The human Y chromosome is here to stay, Nature, viewed 19th March 2012,                <>

France-Presse, A 2007 The insurmountable barrier to cloning primate cells has been breached, thanks to a new technique developed using rhesus monkey cells. COSMOS Magazine, viewed 19th March 2012 <

Hughes, J. F. 2012. ‘Strict evolutionary conservation followed rapid gene loss on human and rhesus Y chromosomes’ Nature. Vol. 483, No. 7387. Viewed 19th March 2012 <>

Marsh, G & Smith, K 2012, Doomed to Extinction, Podcast, Nature, viewed 19th March 2012,                 <>

Trafton, A 2010 Y Chromosome evolving rapidly MITNews, viewed 19th March 2012 <>


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