Non-Mendelian inheritance is a type of biological inheritance wherein the patterns of phenotypes do not accord with those as expected in Mendelian laws on inheritance. It includes extranuclear inheritance, gene conversion, infectious heredity, genomic imprinting, mosaicism, and trinucleotide repeat disorders.
Genomic imprinting is a form of non-Mendelian inheritance. It is when the phenotype of the offspring depends on the source of the chromosome containing the imprinted gene whether it is from the female or from the male parent. Epigenetic factors can cause genomic imprinting. An imprinted gene is one in which the DNA is methylated. When methylated, gene expression is suppressed.
Methylated genes are acquired at fertilization. As the zygote develops into a fully grown organism, its somatic cells will bear the same methylated genes. At the time that the organism produces its own gametes, the imprinted genes are un-methylated. Nonetheless, genomic imprints would be re-instituted in its genome. The location of gene methylation would depend on the sex of that organism. The new gene imprints would consequently affect the phenotype of its progeny. The effect would rely upon the sex of that organism transmitting the chromosome containing the methylated gene (i.e. whether it is a female or male parent).