What term is used for pairs of genes that are different?

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

Answer: (A)

The term "heterozygous" refers to pairs of genes that are different. In the context of genetics, organisms can inherit two different versions, or alleles, of a gene—one from each parent. When these alleles are different, the organism is described as heterozygous for that particular gene. This genetic variation is important as it contributes to the diversity of traits observed in populations, affecting everything from physical characteristics to susceptibility to diseases.

In contrast, the term "homozygous" is used when an organism has two identical alleles for a specific gene, meaning there is no variation at that locus. "Identical" does not have a specific classification in genetics regarding allele pairs but generally suggests sameness, which is not applicable here. "Recessive" refers to an allele that is masked by a dominant allele and does not describe the relationship between two different alleles. Thus, heterozygous is the precise term that captures the essence of having different gene pairs.