I will show you a simplified method using a Punnet Square to predict a dihybrid cross when observing the passage of 2 genes.
The traditional Punnet Square using a monohybrid cross is usually quite simple, but you can get confused with dihybrid crosses if you do not understand the laws that govern them. Take a quick look at my article about Mendel’s Laws if you are not familiar with them.
A simple example of a dihybrid cross
A simple example of a dihybrid cross we can predict is the breeding of 2 Aliens. Find the genotype and phenotype of the offspring if both Aliens are heterozygous for beady eyes (E) and green skin (S)?
Step 1. Find the genotype of the parents
Since the parents are heterozygous( different alleles) this means the parents have a genotype:
Ee – for the eyes
Ss – for the skin.
Step 2. Fill in the Punnet Square
What the Punnet Square does is list every combination possible. E-S, E-s then e-S, e-s.
How we would use this in real life?
What I didn’t mention is these Aliens landed in New Mexico in 1989, and a baby was about to be born. From what we knew about their species, only Martians with normal eyes (ee) and normal skin (ss) could survive the harsh conditions of our plant. What are the chances their single alien child will survive?
In this case the alien child has a 1 out of 16 chance of surviving. 1 out of the 16 boxes has the combination eess.