Despite flash, males are simple creatures

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Genetic simpletons
That's not the case with males.

"We find direct evidence that the expression of the genes on the X has this covering behavior in females whereas in males they're out in the open," said study team member Lauren McIntyre, also of UF.

Males only have one X chromosome, so what you see is what you get. If that particular gene gives the male a boost in terms of sexual selection, say a gene responsible for fluffier feathers, the gene would be selected for in the game of natural selection over successive generations. But if the gene is no good for males, it would get selected against over time.

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"Having one X means your genes are more open to selection in males," UF researcher Marina Telonis-Scott said in a telephone interview. "So in a female if you have a recessive allele that confers a sickness, it can be concealed within the two X's but if you've only got one, such as the male, you're more open to selection."

And the reason males are genetic simpletons, it turns out, is sex. The researchers suggest this uncomplicated (compared with females) genetic pathway allows males to respond at the drop of a hat to the pressures of sexual selection. That way they can win females, produce more offspring and start the cycle over again.

While not as prominent a trend, they also found a similar pattern in so-called autosomal genes, which are those found on any chromosome save the sex chromosomes. Many of the fruit-fly autosomal genes, however, did work in concert with genes located on the X chromosome.

Human implications
The "elephant lurking in these results," of course, is how they would apply to men and women.

The researchers caution the results don't directly translate to humans. "The X function is thought to be quite different in flies than humans," McIntyre told LiveScience. In humans, one of the X chromosomes gets inactivated in females, though research is finding this inactivation isn't always absolute.

However, the results could help explain differences in symptoms and responses to diseases in men and women, the authors say. Sexual selection does occur in humans, they note. In addition, fruit flies and humans share an evolutionary history, the authors point out, which is the reason why we share more than 65 percent of our genes with the tiny insects.

"If we see a mechanism in flies it may also be true in everything that shares that evolutionary history," McIntyre said.

On a basic level, the genetic machinery works in a similar manner in flies and us.

"There's a health aspect in figuring out differences in gene expression between the sexes," Wayne said. "To make a male or a female, even in a fly, it's all about turning things on — either in different places or different amounts or at different times — because we all basically have the same starting set of genes."

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