Imprinting

It has been observed that some inherited traits do not conform
to the pattern expected of classical mendelian inheritance in
which genes inherited from either parent have an equal effect.
The term imprinting is used to describe the phenomenon by
which certain genes function differently, depending on
whether they are maternally or paternally derived. The
mechanism of DNA modification involved in imprinting
remains to be explained, but it confers a functional change
in particular alleles at the time of gametogenesis determined
by the sex of the parent. The imprint lasts for one generation
and is then removed, so that an appropriate imprint can be
re-established in the germ cells of the next generation.