The allele is an alternative form of a gene at a locus.

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

Answer: (A)

An allele is an alternative form of a gene at a specific position on a chromosome, called a locus. Genes are the units of heredity that occupy loci, and alleles arise from small DNA sequence differences at that locus, allowing different versions of the trait to be expressed. In a diploid organism, you typically have two alleles at each locus—one on each homologous chromosome. This variant form concept distinguishes alleles from the broader structures (chromosome), the observable trait (trait), or the basic unit of heredity (gene).