Question

which term describes a type of trait that is usually expressed only when an organism has two identical alleles for the trait?

dominant

recessive

homozygous

heterozygous

Explanation:

To solve this, we analyze each term:

• Dominant: Expressed with one dominant allele (e.g., in Aa, A is dominant and expressed). So not matching.
• Recessive: A trait expressed only when two recessive alleles (identical) are present (e.g., aa). This fits the description.
• Homozygous: Describes the genotype (two identical alleles, like AA or aa), not the trait's expression condition.
• Heterozygous: Genotype with two different alleles (Aa), so trait expression here is for dominant (usually), not requiring two identical alleles.

Answer:

B. recessive