An organism in which the two copies of the gene are identical — that is, have the same allele — is called homozygous for that gene. An organism which has two different alleles of the gene is called heterozygous. Pea plants can have red flowers and either be homozygous dominant (red-red), or heterozygous (red-white). If they have white flowers, then they are homozygous recessive (white-white). Carriers are always heterozygous.
