What are alleles?

• A. The same versions of a gene that may produce indistinguishable phenotypic effects.
• B. Different versions of a gene that may produce distinguishable phenotypic effects.
• C. Non-coding regions of DNA.
• D. Variants of RNA.

Answer: (B)

Alleles are the different versions of the same gene located at the same place on a chromosome. They arise by mutations and explain why people can carry variations of a gene that may lead to different traits. Each person has two alleles at a gene locus (one inherited from each parent), and the specific pair can influence the phenotype because changes in the DNA sequence can alter the encoded protein or how the gene is regulated. Some allele variants produce different, visible traits; others may produce no noticeable difference depending on dominance and interaction with other genes. This is why we describe alleles as different versions of a gene that may yield distinguishable phenotypic effects. The other options refer to noncoding DNA or RNA-level variants, not to DNA versions of a gene.