Imprinting, and the mysterious loss of imprinting that occurs in some genes after birth, have been implicated in human diseases ranging from cancer to mental illness, according to Dr. Andrew Feinberg, a medical professor at Johns Hopkins University. But there is a second layer of genetic information that we're just discovering. I think it will turn out to be one of the great challenges of genetics during the next five years. Feinberg spoke at a genetics seminar in Batr Harbor. The familiar genetics that Mendel described in his landmark 1865 laws of heredity were based on the idea that genes from each parent are equal.
People inherit one paternal and one maternal copy of genes at fertilization.
Generations of geneticists, from Mendel on, thought each parent's gene had an equal function. Feinberg and other scientists, however, have found that some genes work differently, based on the parent from whom they originate. Imprinting does not affect the chemical composition of the gene. It determines whether a gene will be expressed, so that its chemical instructions are used. Scientists term this an epigenetic event, and talk of the epigenome, a set of what may be hundreds of genes whose function is determined by imprinting.