What is a variation of a gene's nucleotide sequence known as?

A variation of a gene's nucleotide sequence is known as an allele. Alleles are different versions of the same gene that can produce variations in traits among individuals. For example, a gene that determines flower color in plants may have different alleles that result in red, blue, or yellow flowers. The variations arise due to changes in the nucleotide sequence, which can affect how the gene is expressed and ultimately influence an organism's characteristics.

In genetics, the concept of alleles is crucial because it explains the diversity seen in traits within a population. Alleles can be dominant or recessive, determining which traits are expressed based on the combination of alleles present in an individual. This genetic variation is the foundation of evolutionary processes and helps populations adapt to changing environments.

Other terms do not capture this specific idea. A gene refers to a segment of DNA that codes for a specific trait, but it does not indicate the variations within that gene. A chromosome is a structure that contains many genes, and a trait is an observable characteristic influenced by genes, but neither of these terms denotes the variations themselves. Therefore, the definition of an allele as a variation distinguishes it as the correct term in this context.