Summary

Epigenetic inheritance refers to heritable characteristics that are controlled by changed in gene expression rather than differences in underlying DNA sequence. Epigenetic inheritance often depends on changes in chromatin state that can be transmitted through mitosis to daughter cells. Molecularly, this may depend on modifications of histone tails – acetylation and methylation were discussed in this chapter, although there are other covalent modifications seen in chromatin. Acetylation of histones is associated with active transcription of nearby genes, while methylation has more varied effects. Methylation of cytosines at CpG sequences in the genome is also associated with decreased transcription of nearby genes.

These epigenetic marks may be inherited through mitosis, and epigenetic silencing of genes plays a role in the development and aging of somatic cells. Accumulation of epigenetic marks happens over the course of a lifetime and is influenced by environment, diet, behavior, and lifestyle. These epigenetic marks are usually, but not always, cleared and “reset” in gametes and/or the fertilized embryo, and new marks are acquired as the cells divide and age. However, some marks persist through meiosis and fertilization. These persistent epigenetic marks include but are not limited to imprinted genes, which are genes that are only, or mostly, expressed from either the paternal or maternal chromosome rather than both chromosomes equally. Transgenerational epigenetic inheritance may influence phenotypes like growth and metabolism, schizophrenia, and depression.