Which term describes a pair of genes?

The term that describes a pair of genes is "allele." In genetics, alleles are different versions of a gene that may produce distinguishable effects. For example, in the context of a specific trait, an organism might inherit one allele from each parent, resulting in a pair of alleles for that trait. This pairing is crucial for determining the genetic makeup and traits expressed in an individual.

While the other terms are related to genetics, they refer to different concepts. A chromosome is a structure within cells that contains many genes, not specifically referring to a pair. A genotype refers to the genetic constitution of an individual, encompassing all the alleles present, not just a pair. Phenotype, on the other hand, describes the observable traits expressed by an organism, which result from the interplay of genotype and environmental factors, rather than the gene pair itself. This distinction highlights why "allele" is the precise term for a pair of genes.