The term that defines a gene made up of two different alleles is heterozygous.

Here's a breakdown:

* Allele: A variation of a gene. For example, a gene for eye color might have alleles for blue eyes, brown eyes, or green eyes.

* Heterozygous: Describes an individual with two different alleles for a particular gene.

For example, if a person has one allele for blue eyes and one allele for brown eyes, they are heterozygous for eye color.