We all have 23 pairs of chromosomes in our cells. For each pair, one came from mother and one from father. Thus, we inherit one copy of each gene from each parent and we generally assume that the function of the gene does not to depend on which parent it came from. However, for imprinted genes things are different. For these genes, either the maternal or paternal copy of the gene is active, while the other one is kept silent. There are at least 80 imprinted genes in humans and mice, many of which are involved in growth of the embryo or the placenta. How can one copy of a gene be switched off, while the other copy in the same cell is switched on? The answer is epigenetics. Probably the most studied imprinted gene is IGF2. One part of IGF2 operates as a switch. If the DNA is methylated here the IGF2 gene can be expressed. The switch is only methylated in Dad’s copy of the gene and so only this copy is expressed, while the maternal copy is silent. This switch is thought to be set up in the gametes (eggs and sperm) so right from the start, genes received from Mum and those from Dad are labelled differently with epigenetic tags and so are not equivalent.
Write a comment