A pair of genes that control a trait is referred to as?

1. Analyze the question The question asks for the term used for a pair of genes that control one trait, such as height or seed shape.

2. Explain the concept

• A gene is a unit of heredity that controls a trait.
• Genes controlling the same trait occur in pairs, one from each parent, at the same position (locus) on homologous chromosomes.
• Each member of such a pair is a form of the gene, and these alternative forms are called alleles.
• Example: for seed shape, the allele R (round) and the allele r (wrinkled) are alleles of the same gene.

3. Go through the options

• A. An allele: This is the term used for the paired or alternative forms of a gene controlling a trait. In JAMB's wording, "a pair of genes controlling a trait" refers to alleles (allelomorphs).
• B. Recessive: This describes a gene whose effect is hidden when a dominant allele is present. It describes expression, not the pair itself.
• C. Dominant: This describes a gene whose effect shows even when only one copy is present. It is also about expression, not the pair.
• D. A hybrid: This is an organism that has two different alleles for a trait (heterozygous), such as Rr. It describes the individual, not the gene pair.

4. Answer The correct option is A, an allele.

5. Exam tip Remember: Allele = Alternative form of a gene at the same locus. Dominant and recessive describe how alleles behave, and hybrid describes the organism carrying two different alleles. If the question says "pair of genes for a trait," think alleles.