Epigenotype

Epigenotype is a term historically used to describe the heritable, non-genetic information that governs gene expression within a cell or organism. It denotes the epigenetic state or regulatory landscape that interacts with the DNA sequence (genotype) to produce a phenotype. In modern usage, epigenotype is often subsumed by the broader concept of the epigenome, but it can be used to emphasize the regulatory layer that is superimposed on the genome.

Epigenetic marks include DNA methylation, histone modifications, nucleosome positioning, chromatin accessibility, and non-coding RNA activity. These marks influence whether genes are turned on or off and how they respond to signals. They are dynamic, changing during development, differentiation, and in response to environmental factors such as diet, stress, toxins, and aging.

Inheritance: Many epigenetic marks are reset during early development; however, some marks are maintained through cell divisions in somatic lineages. Certain loci, such as imprinted genes and some transposons, can transmit epigenetic information across generations, a phenomenon known as epigenetic inheritance. The extent and mechanisms of transgenerational epigenetic inheritance in humans remain an area of active study.

Applications and relevance: Epigenotype plays a central role in development and cell identity, and is implicated in diseases like cancer, neurological disorders, and autoimmune diseases. Techniques to study the epigenotype include bisulfite sequencing for DNA methylation, ChIP-seq for histone marks, ATAC-seq for chromatin accessibility, and whole-epigenome profiling.

Limitations: Epigenotype is tissue-specific and context-dependent; many epigenetic marks are reversible and influenced by environment, making prediction of phenotypic outcomes complex.