Here's a breakdown:

* Alleles: Different versions of the same gene. For example, a gene for eye color might have an allele for brown eyes and an allele for blue eyes.

* Heterozygous: Having two different alleles for a gene.

* Homozygous: Having two identical alleles for a gene.

Example:

Let's say the gene for eye color is represented by the letter "E".

* A person with two brown eye alleles (EE) would be homozygous dominant for brown eyes.

* A person with two blue eye alleles (ee) would be homozygous recessive for blue eyes.

* A person with one brown eye allele and one blue eye allele (Ee) would be heterozygous for eye color. They would likely have brown eyes, as brown is dominant over blue.

Key Point: Heterozygous organisms carry both a dominant and recessive allele for a specific trait. This means they express the dominant trait but also carry the recessive allele that can be passed on to their offspring.