3.20—Phenotype, environment and epigenetics

An organism’s phenotype results from the interaction between its genotype and its environment. Epigenetic modifications can change which genes are expressed without changing the DNA sequence itself.

DNA methylation can reduce transcription, while histone acetylation loosens chromatin so transcription factors and RNA polymerase can access genes. These changes alter mRNA and protein production, and some can persist through cell division.

Genetically similar plants can differ in height when water or mineral supply differs. A lifestyle or environmental signal can also change gene expression through epigenetic tags, but that is not the same as creating a new allele.

An environmentally changed phenotype is not automatically inherited. Distinguish a reversible epigenetic state from a mutation in the DNA sequence, and state which evidence supports inheritance across cell division.