New fertility techniques have enabled men with low sperm counts to father children. But it appears that sons born to some of these men may also be infertile. An estimated 10-15 per cent of all men, who can produce little or no sperm, suffer from a genetic defect in a part of the Y chromosome known as the AZFc. When these men father children through in-vitro fertilisation (ivf) techniques, their sons tend to inherit the genetic defect. Daughters are not affected as females receive from their fathers an X chromosome instead of the Y chromosome. David C Page, a researcher at the Whitehead Institute says that although IVF may help otherwise infertile men have children, it may not ensure that there eventually will be grandchildren ( Human Reproduction , Vol 14, No 6).