What is a dominant and recessive allele (and trait)

(please help!)

The principle of dominance states that some alleles are dominant and others are recessive. An organism with a dominant allele for a particular form of a trait will always exhibit that form of the trait. An organism with a recessive allele for a particular form of a trait will exhibit that form only when the dominant allele for the trait is not present.

Explanation:

  Dominant                 T     t

    TT Tt Tt             T   TT  Tt

 Recessive=           t   Tt   tt

        tt