Genetic imprinting and gene silencing
Gold, M. 2006.  BH 16:19-31. CELD ID 21474

The genetic expression of a small number of the 30,000 or so genes in human cells is not derived from both inherited parental chromosomes, but is exclusively expressed from either the maternal or the paternal partner. This process, whereby only one version of a gene is expressed, depending on whether it was passed on to the fetus through the egg or the sperm, is called genetic imprinting. Imprinting is a reversible modification of DNA that can lead to differential expression of maternally or paternally inherited genes. Since this process adds additional information to the DNA sequence, it has been called "epigenetics" (epi=on). Our Sages described genetic imprinting a long time ago when they revealed the source of some human characteristics as coming directly from G-d, others from the father, and others from the mother. We now understand how this differentiation works. There are two proposed mechanisms from the differentiation, each backed by experimental evidence: the postreplicative methylation of specific DNA cytosine residues; and post-translational modification of histones. It is not yet clear if these mechanisms are universal. The hidden fingerprints of the Divine are thus found in the pattern of human development at the molecular level.