One of the alternative forms of a gene that governs a trait is called what?

• A. Locus
• B. Gene
• C. Chromosome
• D. Allele

Answer: (D)

Alleles are the alternative forms of a gene at the same place on a chromosome that can influence a trait. They are versions of the gene’s sequence that may lead to different phenotypes—for example, different versions that code for light or dark coloration. A gene is the basic unit of heredity, the locus is the specific position on the chromosome where that gene resides, and the chromosome is the structure that carries many genes. Since organisms are typically diploid, you inherit two alleles for each gene (one from each parent), which can be the same or different and can show dominance or recessiveness in trait expression.