Sex and the X
The X chromosome generates and receives more new genes by retrotransposition
than autosomes
By Cathy Holding

Mammalian sex chromosomes are thought to have evolved specifically to carry
sex-related genes. Now, researchers have shown that retrotransposition is
facilitating the sex-related gene abandonment of the X chromosome in favor
of the autosome.

In January 30 Science, J. Emerson and colleagues at the University of
Chicago examined gene movement and observed that a disproportionate number
of genes involved in sex determination and function have abandoned the X
chromosome, ignored the Y, and relocated to autosomes to function in a male
sex-biased fashion. Conversely, genes having a non-sex determining role
relocated to the X chromosome (Science, 303:537-540, 2004).

"This was really unexpected," Manyuan Long, the team leader, told The
Scientist. "An excessive number of genes show a trend to avoid being linked
to the X chromosome and have evolved new male-specific expression patterns
on the autosome. On the other hand, genes move to the X chromosome to avoid
anything to do with female sex. There are two directions of gene creation,"
he said.

In 2002, the team reported unexpected unidirectional gene movement from the
X chromosome to autosomes in fruit flies. In this study, the team screened
the human genome databases for annotated genes with functional
retrotranspositions on different chromosomes and found 94 functional
retroposed gene pairs that were not on the same chromosome. Similar
screening in the mouse revealed 105 such gene pairs. Their analyses showed
that the X chromosome generates an almost 300% excess of retrogenes compared
with autosomes in humans, and 305% in the mouse.

"This has raised a lot of new questions," said Long. "When a
sex-related
gene is trying to abandon the X chromosome for an autosome, what is the
point of having the X and the Y? This is completely different to previous
speculation."

Read the rest at The Scientist.com
http://www.biomedcentral.com/news/20040202/01

Comment:
By and by, Y goes awry: why?

Posted by
Robert Karl Stonjek.
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