Punnett squares are used to show genetic crosses. Dominant alleles are capitalised e.g. A, recessive alleles are shown in lower case e.g. a. For Co-dominant alleles, a capital letter and superscript is used e.g. ABO blood group which has multiple alleles: IA,IB (co-dominant) and IO (recessive). Gametes are shown as headings in a two-way table and the combinations shown in the cells.The gametes represent the possible genotypes of haploid gametes after meiosis and the combinations shown in the cells represent the possible diploid combinations of the offspring after fertilisation.Monohybrid inheritance shows just one gene being crossed e.g. Gg whilst dihybrid crosses show two different genes GgRr.