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Ladies First: Genes skew sex ratios in evolutionary struggle

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1:30pm, November 7, 2007

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.

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