Magazine article Science News

Ladies First: Genes Skew Sex Ratios in Evolutionary Struggle

Magazine article Science News

Ladies First: Genes Skew Sex Ratios in Evolutionary Struggle

Article excerpt

Competition among genes within an individual male fruit fly can cause its sperm to produce a high proportion of female offspring. Now, scientists have identified a gene responsible for this well-known phenomenon as well as the gene that later evolved to restore gender balance.

In essence, the two fruit fly genes engage in a tug-of-war in which each succeeds evolutionarily if it can spread widely among future generations.

The imbalance favoring females happens because the sex-skewing gene, called Distorter on the X (Dox), is located on the X chromosome. Females each have two X chromosomes, and pass on only Xs to their offspring. Males each have an X and a Y. They pass an X chromosome to their female offspring and a Y to their male offspring.

To ensure its evolutionary success, Dox somehow sabotages the maturation of sperm carrying Y chromosomes. As a result, a male fruit fly carrying Dox would produce a generation of offspring that is more than 90 percent Dox-carrying females.

This imbalance allows Dox to spread widely among a population in only a few generations, but the gene's success sets the stage for its own defeat.

Once the population is dominated by females, a male will have many chances to reproduce and pass on its genes. This fact changes the game, because it means that a gene can now spread rapidly if it's carried by a male.

The preponderance of females "creates a strong pressure for the evolution of a [Dox] suppressor gene," says Yun Tao of Emory University in Atlanta, who led the research. …

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