Differentiate between a gene and an allele.

• A. A gene is a DNA sequence that encodes a protein.
• B. A gene is a unit of heredity; an allele is a variant form of a gene.
• C. A gene is a chromosome; an allele is a gene.
• D. A gene is a mutation type; an allele is a gene product.

Answer: (B)

A gene is the basic unit of heredity, a specific DNA sequence at a particular spot on a chromosome that carries the information to make a functional product, such as a protein or RNA. An allele is a variant form of that same gene, arising from sequence differences at that locus and potentially leading to different versions of the trait. In diploid organisms you have two alleles for each gene, which can be the same or different, and the combination influences the phenotype. For example, a gene for flower color might have a red allele and a white allele, with dominance determining the visible color. The other statements misrepresent the relationships: a gene is not a whole chromosome, and not all genes encode proteins, while an allele is not itself a separate gene or a product by itself.