Scientists have found other examples of imprinted genes, but none quite this dramatic.

And in recent years, some medical disorders in humans have been tied to these imprinted genes.

Dr. Haig's work is now widely hailed for making sense of imprinted genes.

It turns out that a number of imprinted genes are active in the brain, where they might influence how babies behaved toward their mothers.

Because these so-called imprinted genes must be methylated to function, they are vulnerable to diet and other environmental factors.

Investigators say they still do not know by what chemical or physical mechanism the imprinted genes are masked.

It is an imprinted gene, expressed from the maternal allele.

Various methods have been used to identify imprinted genes.

Further research showed that within these regions there were often numerous imprinted genes.

His theory would not predict an effect of imprinted genes on maternal behavior such as removing the placenta, he said.