Technique for separating sperm by sex

Scientists in Japan have developed a technique for separating sperm by sex, using it to produce litters of mice, pigs and cows in which around 90% of offspring conform to the desired sex. And they admit the technique, outlined in PLOS Biology, could potentially be applied to humans, making it possible for those undergoing IVF to select their child’s sex prior to fertilisation.

The team, from Hiroshima University, chanced upon the method while studying the differences between X (female) and Y (male) sperm cells in mice. Sperm with X chromosomes, they discovered, carry more genes than Y ones, and so produce a wider range of protein receptors. When they used a chemical to bind to the X sperm’s receptors, they found that the sperm swam more slowly – enabling them to be separated from Y sperm.

The technique could be used to make the dairy industry more humane, by reducing the number of surplus males (many of which are slaughtered at birth). But if human sperm are found to contain the same receptors, it could also make it possible for IVF clinics to produce embryos of a selected sex. Embryos produced by IVF can already be screened for sex – and in some countries, including the US, growing numbers of parents are using this method to choose a child’s sex. However, the new technique could hugely extend sex selection, and raises ethical concerns. “Sex skewing in humans would be an ethical minefield with the potential for unpredictable and disruptive social consequences,” said Dr Peter Ellis, a molecular biologist at the University of Kent.