Which term describes an organism that has two different alleles for a particular trait?

The term that describes an organism possessing two different alleles for a particular trait is "heterozygous." In genetics, alleles are different versions of a gene that can exist at a specific locus on a chromosome. When an organism has one allele from each parent that are different, it is classified as heterozygous.

For example, consider a trait like flower color, where one allele might be for red flowers and another for white flowers. If a plant carries one allele for red flowers and one for white flowers, it is heterozygous for that flower color trait. This genetic makeup can influence how the trait is expressed, depending on whether one allele is dominant over the other.

The other terms refer to different concepts: "homozygous" means having two identical alleles for a trait, while "dominant" and "recessive" describe the relationship between alleles—where a dominant allele can mask the expression of a recessive allele in the presence of both. Thus, heterozygous specifically captures the essence of having two different alleles for a trait.