Eye Color example: Which describes an allele?

• A. A non-coding region.
• B. A chromosome.
• C. The entire genome.
• D. A variant form of a gene that contributes to a phenotype.

Answer: (D)

An allele is a variant form of a gene. Genes are instructions that can produce a product influencing a trait, and different versions of the same gene—alleles—can lead to different phenotypic outcomes. In eye color, certain genes have multiple alleles that affect pigment production, producing shades from blue to brown. The key idea is that an allele is a specific version of a gene that can contribute to how a trait appears.

The other options aren’t alleles because a non-coding region is a stretch of DNA that may regulate genes but isn't a version of a gene itself, a chromosome is a structure that carries many genes, and the entire genome is all genetic material. Each of those describes different genomic concepts, not an allele.