Epigenetics is-

Ans. is 'c' i.e., Alteration in gene expression* Epigenetics is a heritable change in the level of gene expression, not caused by changes in DNA sequence.* It includes changes like Histone modification or DNA methylation# Covalent modifications of either DNA (e.g. cytosine methylation and hydroxymethylation) or of histone proteins (e.g. lysine acetylation, lysine and arginine methylation, serine and threonine phosphorylation, and lysine ubiquitination and sumoylation) play central roles in many types of epigenetic inheritance.* Histone acetylation is found to cause uncondensation of chromsosomes. Uncondensed chromosomes are more prone to get expressed. Hence Histone acetylation is found to increase the level of gene expression* Methylation of Cytidine of CG islands is found to cause condensation of chromosomes. This in turn decreases the level of gene expression* Epigenetic alterations are preserved during cell division. It is also propogated to progeny by a process called as transgenerational epigenetic inheritance* Thus epigenetics is a heritable change in the levels of gene expression not mediated by changes in DNA or gene sequence.