Two different alleles of the same gene are called what?

• A. Homozygous
• B. Heterozygous
• C. Dominant
• D. Recessive

Answer: (B)

Think about genotype as the two versions of a gene that an organism has, one from each parent. When those two versions are different, the genotype is described as heterozygous. That means you’re carrying one form from one allele and a different form from the other allele for the same gene.

This is distinct from homozygous, where both copies are the same. Dominant and recessive describe how a trait appears, not whether the two alleles are the same; a heterozygous individual can show the dominant trait even if a recessive version is also present, depending on which allele is dominant.

For example, if one allele for a trait makes a certain color and the other allele makes a different color, the individual with one of each is heterozygous and, depending on dominance, will display one of those colors in the phenotype.