Final answer:
Epigenetic modifications are heritable changes in gene expression that occur without changes to the DNA sequence, through mechanisms like DNA methylation and histone acetylation.
Step-by-step explanation:
Epigenetic Modifications
Epigenetic modifications are heritable changes in gene expression that do not entail alterations to the DNA sequence itself. Instead, they involve chemical changes to DNA or to the histone proteins around which DNA is wrapped, such as methylation and acetylation. These modifications can affect how genes are turned on or off and are often a response to environmental stimuli. For example, histone acetylation typically leads to a loosening of the DNA-histone structure, resulting in increased gene expression. Conversely, DNA methylation is usually associated with a decrease in gene expression.
Environmental factors like ultraviolet light can trigger epigenetic changes that alter gene expression. These changes can be passed down to subsequent generations, affecting the phenotype without changing the underlying genetic code.