An organism with 2 alleles for 1 trait that are different is called a heterozygote.

Here's a breakdown:

* Allele: A variant form of a gene.

* Trait: A specific characteristic of an organism.

* Heterozygote: An individual with two different alleles for a particular trait.

For example, let's say we're looking at the trait of eye color. A person with one allele for brown eyes (B) and one allele for blue eyes (b) would be considered a heterozygote. Their genotype would be Bb, indicating that they carry both alleles.