Question

How do I represent dominant or recessive alleles?

Answer 1

Dominant is represent by capital Letter and recessive is represented by lower case letters

Such as BB (for homozygote dominant) Bb (heterozygote - both dominant and recessive) and bb (for homozygote recessive)

Answer 2

There are only two possible alleles, of which just one is recessive, one of the dominant. Implicit gene habits are expressed in lowercase letters, and the corresponding dominant genes are represented by the corresponding capital letters.
That's the answer, my dear~