Is imprinting important?
Yes. • Deliberate (in mice) or accidental (in humans) inheritance of two copies of a particular chromosome from one parent and none from the other parent is usually fatal (even though a complete genome is present). • Inheritance of two copies of one of mother’s genes and no copy of the father’s (or vice versa) can produce serious developmental defects. • Failure to inherit several nonimprinted genes on the father’s chromosome #15 causes a human congenital disorder called Prader-Willi syndrome. • Failure to inherit one nonimprinted gene (UBE3A) on the mother’s chromosome #15 causes Angelman syndrome. • Failure of imprinting in somatic cells may lead to cancer. • The cancerous cells in some cases of a malignancy called Wilms´ tumor and many cases of colon cancer have both copies of the IGF2 gene expressed (where only one, the father’s, should be). • Reduced methylation — and hence increased expression — of proto-oncogenes can lead to cancer, while • increased methylation — and hence decr
