The difference between heterozygous and homozygous individuals lies in the alleles they carry in their genes.

Explanation:

Heterozygous and homozygous are terms used to describe the genetic makeup of an individual with respect to a particular gene or trait.

Homozygous individuals have two copies of the same allele (variant of a gene)(RR or rr) for a particular gene. In other words, both of their alleles are identical. Homozygous individuals can be either homozygous dominant (both alleles are dominant) or homozygous recessive (both alleles are recessive).

Heterozygous individuals have two different alleles (Rr) for a particular gene, one inherited from each parent. Heterozygous individuals are typically carriers of a recessive allele, but do not exhibit the trait associated with the recessive allele because they have a dominant allele that masks the recessive one.

For example:

If we consider the gene that controls eye colour, one allele may code for brown eyes and another allele may code for blue eyes. An individual who is homozygous for brown eyes will have two copies of the brown eye allele.

An individual who is heterozygous for eye colour will have one brown eye allele and one blue eye allele, and their eye colour will depend on the dominance relationship between the two alleles.