Heterozygous - Having two different genes (e.g., A and a) at the corresponding gene loci on homologous chromosomes.That is, different chromosomes that relate to the same characteristic. The two genes in this case are different - one is recessive, the other dominant.

Homozygous - Having identical genes (e.g., AA or aa) at the corresponding gene loci on homologous chromosomes. That is, different chromosomes relating to the same characteristic. The two genes in this case are identical - both recessive, or both dominant.

Homologous - Showing a fundamental similarity of structure because they have been inherited from a common ancestor. Applied to structures ranging from organs to molecules.
Body parts are considered homologous if they have

• the same basic structure
• the same relationship to other body parts, and, as it turns out,
• develop in a similar manner in the embryo

The following picture of a chromosone demonstrates a homologous chromosone.

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