What term defines a gene made up of two different alleles?

recessive

heterozygous

segregated

homologous

Option B , heterozygous

Explanation:

A heterozygous allele pair (gene) consists of two different alleles for the same trait (such as height, color, texture etc.)

For example -

Let "R" represents the allele for red color of flower

and "r" represent the allele for white color of flower

Then Allele pair "RR" and "rr"  are called as homologous allele pair having same kind of alleles

While the allele pair "Rr" represents the heterozygous allele pair.

Hence, option B is correct