* Capital letters represent dominant alleles. For example, "B" might represent the dominant allele for brown eyes.

* Lowercase letters represent recessive alleles. For example, "b" might represent the recessive allele for blue eyes.

Here's how you might represent different allele combinations:

* Homozygous dominant: Two copies of the dominant allele. Example: BB (brown eyes)

* Heterozygous: One dominant and one recessive allele. Example: Bb (brown eyes, because brown is dominant)

* Homozygous recessive: Two copies of the recessive allele. Example: bb (blue eyes)

Important notes:

* The specific letters used can vary depending on the trait being considered.

* The choice of dominant vs. recessive is based on the trait's expression in a heterozygous individual. The dominant allele is the one that is expressed.

Let me know if you'd like to see some examples of how alleles are used to represent different genetic crosses!