Question

6. (2 points) How is the process of X inactivation similar to genomic imprinting? How are they different?

Answer 1

The genomic imprinting is silencing some regions of the genome or only one copy of gene is expressed and the other silenced. The DNA received from parents contain one copy of a gene from father and one copy from mother. Sometimes, the copy of gene expressed is always the copy received from the father. This could be a mechanism of epigenetic gene regulation. The genome imprinting depends on the differences in the pattern of methylation of maternal or paternal genes. Some genes may also involve histone protein modifications. The genomic imprinting has been found in different forms in animals, plants and fungi while in humans only 1% genes are regulated by genome imprinting.

The X inactivation on the other hand is the silencing the expression of entire X chromosome. The X chromosome is received as one copy from the father and two copies from the mother. The females have two copies of X chromosome in every cell and its inactivation is complicated process. The compact X chromosome that becomes transcriptionally inactive and is known as Barr body. The X inactivation is also a mechanism of epigenetic regulation and is mediated by small RNAs. For example, the mosaic pattern of skin in tortoise shell cats is due to X chromosome expression received from father while the X chromosome received from mother is inactivated or not expressed (silenced).