An organism that has two different alleles for a particular trait is called a heterozygote.

Here's a breakdown:

* Allele: An alternate form of a gene.

* Heterozygous: Having two different alleles for a specific gene.

* Homozygous: Having two identical alleles for a specific gene.

For example, if a flower has one allele for red petals (R) and one allele for white petals (r), it would be heterozygous for petal color. Its genotype would be Rr.