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The battle of the sexes rages in the most unexpected places. Mothers' and fathers' genes fight for supremacy even outside the womb, say American researchers. They have discovered that marsupials, like placental mammals, have imprinted genes for growth, although their young spend only a short time in the uterus before crawling into their mother's pouch.
Imprinted genes are expressed only if they are inherited from a particular parent. For instance, IGF2, the gene for a growth factor that leads to bigger babies, is only expressed in humans if it comes from the father. However, M6P, which opposes IGF2, is only expressed if it comes from the mother.
Genes such as these are thought to have evolved because fathers want big babies that hog nutrients, especially if they share womb space with siblings that may have different fathers -- a common phenomenon in primitive mammals. "Half the shrews near Oxford carry biparental litters," says Chris Graham, who studies genetic imprinting at Oxford University. Mothers, meanwhile, want smaller, less demanding babies (New Scientist, 3 May 1997, p 34).
Randy Jirtle and his colleagues at Duke University in North Carolina didn't expect genes to be imprinted in marsupials, whose embryos spend a very short time in the womb. After only a few days of initial development, the tiny offspring crawl to the mother's pouch and latch onto nipples, where they stay until birth. Nor should the genes appear in monotremes, where after a brief spell inside, the young are laid in eggs.
The team, together with Barry Munday at the University of Tasmania, measured gene expression in two monotremes
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Contact: Claire Bowles
claire.bowles@rbi.co.uk
44-207-331-2751
New Scientist
9-May-2000