Ofigure out the outcome of a cross, set up a punnett square.
a. put the gametes of one parent at the top and those of the other on the left. to determine the allele(s) in each gamete for a given genotype, set up a systematic way to list all the possibilities. (remember, each gamete has one allele of each gene.) note that there are 2n possible types of gametes, where n is the number of gene loci that are heterozygous. for example, an individual with genotype aabbcc would produce 23 = 8 types of gametes. write the genotypes of the gametes in circles above the columns and to the left of the rows.
b. fill in the punnett square as if each possible sperm were fertilizing each possible egg, making all of the possible offspring. in a cross of aabbcc × aabbcc, for example, the punnett square would have 8 columns and 8 rows, so there are 64 different offspring; you would know the genotype of each and thus the phenotype. count genotypes and phenotypes to obtain the genotypic and phenotypic ratios. because the punnett square is so large, this method is not the most efficient.