Final answer:
Epigenetic changes are modifications that affect gene expression without altering the DNA sequence. These changes, such as histone acetylation and DNA methylation, can be heritable and are influenced by environmental factors. They occur at various levels including epigenetic, transcriptional, and translational, and are distinct from genetic mutations which change the DNA sequence.
Step-by-step explanation:
Epigenetic changes are modifications that affect gene expression without altering the DNA sequence itself. These changes occur through mechanisms such as methylation, phosphorylation, and acetylation of DNA and histone proteins. Environmental factors like ultraviolet light can trigger epigenetic changes, leading to alterations in how DNA is accessed and transcribed. For example, histone acetylation typically results in relaxed chromatin structure, making the DNA more accessible for transcription, whereas methylation can cause chromatin to condense, silencing gene expression.
Epigenetic modifications are often heritable, meaning they can be passed down from one generation to the next. While they do not change the DNA sequence itself, these modifications can have lasting effects on organisms. For instance, lifestyle factors such as smoking or diet can induce epigenetic changes that may affect not only an individual's gene expression but potentially those of their offspring as well. However, contrary to some beliefs, epigenetic modifications are not always heritable and some can be reversible. They also do not happen solely during transcription, but can be present at the epigenetic, transcriptional, and translational levels.
Since epigenetic changes do not involve a mutation in the DNA sequence, they differ fundamentally from genetic mutations. A mutation involves a change in the nucleotide sequence of DNA, which can lead to changes in the mRNA and protein produced, possibly resulting in a different phenotype. However, both genetic and epigenetic changes contribute to an organism's phenotype and can be influenced, either directly or indirectly, by environmental stimuli.