How does an allele differ from a gene?

An allele is indeed a variant form of a gene. A gene is the fundamental unit of heredity that encodes for specific traits and is composed of DNA. Alleles arise as different versions of a gene that occur at a specific locus on a chromosome. For example, a gene may determine flower color in a plant with alleles for red or white flowers. These variations can result from mutations and lead to the expression of different traits.

In contrast, the other options do not accurately reflect the relationship between alleles and genes. Describing an allele as a unit of heredity misrepresents its role, as it is actually a specific variant of a gene. The idea that alleles are exclusively found in prokaryotes while genes are in eukaryotes is not correct, as both alleles and genes are present in all forms of life, although their structures and organization may differ. Lastly, stating that genes are variations of traits while alleles are fixed does not capture the dynamic nature of how alleles can exhibit variation.