Alternate versions of a gene are called what?

• A. Genes
• B. Alleles
• C. Chromosomes
• D. Phenotypes

Answer: (B)

Alternate versions of a gene are called alleles. A gene sits at a specific spot on a chromosome and influences a trait. Alleles arise through mutations and are inherited from parents, so for any given gene most individuals have two alleles—one on each chromosome of the pair. If both alleles are the same, the organism is homozygous for that gene; if they are different, it is heterozygous. Alleles can interact in different ways to shape the phenotype: one may be dominant and mask the other, or there can be codominance or incomplete dominance in some traits. Populations often carry multiple alleles for a gene, which increases genetic diversity; a classic example is the multiple alleles seen at the ABO blood group locus.