Final answer:
The second step in constructing a Dihybrid Punnett square is to line up the alleles from the second parent on the left side of the square, which allows for the visualization of all possible allele combinations for offspring genotypes.
Step-by-step explanation:
The second step to make a Dihybrid Punnett square involves taking the alleles (factors) from the second parent and lining them up on the left side of the square. For instance, if dealing with heterozygous purple flowers with genotypes Bb for pod color and Ff for pod shape, the factors from the second parent would be B, b, F, and f.
After listing the factors of the first parent across the top, you align the factors of the second parent on the side. This sets the stage for creating the grid that will allow you to pull the factors from the top into the boxes below and the factors from the side into the boxes next to them. This process will result in the visualization of all possible combinations of alleles and the subsequent prediction of offspring genotypes.