Ch 7 Review Tools A B allele trait dominant expressed trait recessive trait not expressed incomplete dominance neither trait dominates codominance blending heterozygous different alleles homozygous same alleles probability chance of occurrance monohybrid cross cross with one trait dihybrid cross cross with two traits self-pollination self fertilization true-breeding homozygous dominant, recessive genotype set of alleles phenotype physical appearance mutation genetic disorder pedigree chart of family history