Changes in sequence
Copying errors, some environmental influences and other processes can alter DNA, while cells also possess repair mechanisms. Changes may affect one nucleotide or longer stretches. Describing a mutation requires its position and the difference between sequences, making the observation more informative than a general label of genetic change.
Germline and somatic lineages
Germline changes can pass through eggs or sperm to offspring. Somatic changes generally persist within the affected cell lineage rather than being transmitted through reproduction. Timing can leave different sets of cells with different sequences. A mutation’s cellular history therefore influences which tissues and generations contain it.
References: [2]
Sequence and functional consequences
Some changes affect proteins or expression, while others have no obvious consequence for the question under study. Effects can depend on other genes and environmental conditions. Researchers distinguish detecting a variant from demonstrating its function, using comparisons and experiments to investigate relationships with particular observable outcomes.
New changes and inherited variation
A person’s variants may be inherited or arise during germ-cell formation or development. Newly arising and inherited changes have different histories that can be followed through cells and families. Mutation supplies sequence diversity; subsequent reproduction and population processes influence how that diversity persists and becomes distributed.