Final answer:
To set up a dihybrid Punnett square, consider two genes simultaneously and use a grid to represent the possible combinations of alleles. Genotypic and phenotypic ratios can be determined from the Punnett square. For more complex crosses, alternative methods like the forked-line or probability methods may be used.
Step-by-step explanation:
To set up a dihybrid Punnett square, you need to consider two genes or characteristics simultaneously. The Punnett square is a grid with the possible combinations of alleles listed along the top and side. Each box represents the diploid genotype of a zygote that could result from the mating. Both genotypic and phenotypic ratios can be determined from the Punnett square if the pattern of inheritance is known. For complex crosses with more than two genes, the forked-line method or probability methods may be preferred.