Reproduction, Fertility and Development Reproduction, Fertility and Development Society
Vertebrate reproductive science and technology

The degenerate Y chromosome – can conversion save it?

Jennifer A. Marshall Graves

Research School of Biological Sciences, The Australian National University, Canberra, ACT, Australia. email:

Reproduction, Fertility and Development 16(5) 527-534
Submitted: 8 October 2003  Accepted: 15 April 2004   Published: 22 July 2004


The human Y chromosome is running out of time. In the last 300 million years, it has lost 1393 of its original 1438 genes, and at this rate it will lose the last 45 in a mere 10 million years. But there has been a proposal that perhaps rescue is at hand in the form of recently discovered gene conversion within palindromes. However, I argue here that although conversion will increase the frequency of variation of the Y (particularly amplification) between Y chromosomes in a population, it will not lead to a drive towards a more functional Y. The forces of evolution have made the Y a genetically isolated, non-recombining entity, vulnerable to genetic drift and selection for favourable new variants sharing the Y with damaging mutations. Perhaps it will even speed up the decline of the Y chromosome and the onset of a new round of sex-chromosome differentiation. The struggle to preserve males may perhaps lead to hominid speciation.


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