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Sci Tech
Blame it on father
FERTILITY EXPERTS admit they are baffled by the recent discovery of families in which a tendency to sire twins is passed on from father to sons, according to a report in New Scientist. It's a conundrum because there is no obvious mechanism by which sperm can affect the number of babies a woman has.
Usually twins are born because a woman releases more than one egg at a time, or because a fertilised egg splits early in development.
The families share the same surname so they may be related. Some of the twins are identical, others not.
Curiously, some men from the twin families appear to have problems getting their partners pregnant. That hints at one possible cause of the twinning. When a sperm enters an egg, the egg expels a "polar body" containing one set of chromosomes.
The single set in a sperm then combines with the egg's remaining set in the egg nucleus to provide the full complement of chromosomes.
But if two sperm entered the egg, researchers speculate, one could fuse with the egg nucleus and one with the polar body, producing twins. If, on the other hand, two sperm fused with the nucleus, the resulting embryo would have three sets of chromosomes and wouldn't develop far, causing fertility problems.
One problem with the theory, however, is that there's no known way for two sperm to enter a single egg. The team will examine the men's sperm to see if they have unusual characteristics that might allow that to happen.
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