How do dominant and recessive alleles work?

Dominant phenotypes will manifest when either or both chromosomes have the same dominant alleles, whereas recessive phenotypes will only manifest when both chromosomes have the same recessive alleles. Dominant alleles  are shown with a capital letter and the recessive allele with the corresponding small letter. Recessive alleles will be overridden by the presence of a dominant allele. Two recessive alleles (no dominant) need to be present for the recessive characteristic to be expressed in the phenotype .

Dominant + recessive > dominant

Dominant + dominant > dominant

Recessive + dominant > dominant

Recessive + recessive > recessive