Final answer:
Epigenetic changes are heritable alterations in phenotype that do not involve changes in the DNA sequence but affect gene expression. These changes are passed down to daughter cells, influencing various traits and characteristics without altering the underlying genetic code.
Step-by-step explanation:
The heritable alteration in a cell/organism's phenotype without changes in the nucleotide sequences of DNA refers to epigenetic changes. Unlike mutations that involve alterations in the DNA sequence itself, epigenetic changes affect gene expression and can be inherited. These changes can occur due to modifications such as histone acetylation or DNA methylation, which do not change the actual DNA sequence but can influence whether a gene is turned on or off.
Gene expression is a tightly regulated process that determines which genes are active at any given time, leading to different phenotypes despite identical genetic information. Factors such as environmental conditions can cause epigenetic changes, affecting gene expression and consequently the phenotype. For example, exposure to certain chemicals can lead to modifications of the chromatin structure surrounding genes, altering the cells' gene expression profiles and thus their function and appearance. These modifications can be passed down to daughter cells during cell division, thereby constituting heritable phenotypic changes.