FORGET tall, dark and handsome 鈥� smooth, oval and symmetrical is what an egg wants in sperm. Now it seems that the sperm chosen on these grounds to use in assisted reproduction are more likely to carry an X chromosome than a Y.
Couples struggling to conceive may opt for a technique that involves extracting the woman鈥檚 eggs and injecting each with a sperm, chosen after examining them at either 400x or 6600x magnification.
Daniela Braga at the in S茫o Paulo, Brazil, examined 153 embryos fertilised using the lower magnification technique and 240 using higher magnification. She found that sperm had a 64.7 per cent chance of carrying an X chromosome if selected at 6600x magnification, but just a 53.8 per cent of carrying an X if picked at the lower magnification.
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Braga cannot yet explain the effect. 鈥淴 sperm is heavier than Y sperm, but that couldn鈥檛 have made a difference.鈥� She presented the results at the annual meeting of the European Society of Human Reproduction and Embryology in Stockholm, Sweden, this month.