Men can rest easy – sex chromosomes are here to stay
9 May 2012
Fears that sex-linked
chromosomes, such as the male Y chromosome, are doomed to extinction have been
refuted in a new genetic study which examines the sex chromosomes of chickens.
The study, published today in the journal Proceedings of the National Academy of Sciences (PNAS), looked at how genes on sex-linked chromosomes are passed down generations and linked to fertility, using the specific example of the W chromosome in female chickens.
The results confirm that although these chromosomes have shrunk over millions of years, and have lost many of their original genes, those that remain are extremely important in predicting fertility and are, therefore, unlikely to become extinct.
Professor Judith Mank, from the UCL Department of Genetics, Evolution and
Environment and senior author said: “Y chromosomes are here to stay, and are
not the genetic wasteland that they were once thought to be.”
W chromosomes in female chickens are entirely analogous to Y chromosomes in men in that they are sex-limited and do not re-combine when males and females reproduce, as the other regions of the genome do. Recombination allows chromosomes to break up linked genes, which makes selection more effective and helps get rid of faulty mutations. Some scientists think that Y and W chromosomes are doomed because of this lack of recombination.
Y chromosomes are here to stay, and are not the genetic wasteland that they were once thought to be.
Professor Judith Mank
The study, which involved researchers at UCL, Oxford and the Swedish
Agricultural University, compared DNA regions on the W chromosome in different
breeds of chickens, whose fertility rates are very easy to measure simply by
Genetic information from two breeds, the Minorca and Leghorn, which lay more
than 250 eggs per year, were compared with two breeds selected for male traits
(fighting and plumage) called Yokohama and Old English Game. The
researchers also looked at Red Jungle Fowl, a wild ancestor of chickens.
The researchers measured gene expression levels from the W-linked genes in all
the breeds, and showed that selection for laying lots of eggs has led to
elevated gene expression for almost all the W-linked genes in the layer
breeds. At the same time, relaxed female selection in the fighting and
plumage breeds has led to a loss of W gene expression.
This means that female-specific selection related to fertility acts to shape
the W chromosome, and that the chromosome is able to respond to that selection
despite all the problems with the lack of recombination.
Professor Mank said: “We have shown that Y and W chromosomes are very important
in fertility – the Y in males and the W in females. It is the ability of the
W-linked genes to evolve that is the key to their survival, and which suggests
that both the Y and the W chromosomes are with us for the long haul.”
The research was funded by the Biotechnology and Biological Research Council (BBSRC) and the European Research Council.
Media contact: Clare Ryan