It is an epigenetic phenomenon that causes genes to be expressed in a parent-of-origin-specific manner. Expression of certain genes is determined by whether the gene is inherited from the mother or father. Igf2 insulin growth factor is paternal. H19 is maternal.
Methylation and occurs in the sperm and ovum separately before fertilization.
It also controls the expression severity or age of onset of disease depending upon the gender of affected parent point in Huntington disease age of onset of symptoms is lower in people who inherited it from their mother.
McDade 2019. Poverty imprints 10% of genes. Causing chronic inflammation. Cortisol dysregulation and insulin destruction.