IT SOUNDS impossible, but infertility can be inherited. Reproductive
biologists have discovered a gene that makes female sheep sterile when they
carry two defective copies. When they carry only one defective copy, however,
they are superfertile and give birth to twins or triplets, keeping the gene in
circulation.
No one knows whether a similar genetic disorder could affect humans. “The big
question is whether sisters of infertile women are having twins,” says team
leader Susan Galloway of the University of Otago in Dunedin, New Zealand.
Left to their own devices, sheep usually produce a single lamb. But selective
breeding has…
