How do you determine a ratio or probability from a punnett square?

To determine a ratio from a Punnett square, count the occurrences of each genotype or phenotype in the resulting offspring combinations. For example, if the square shows three offspring with a dominant trait and one with a recessive trait, the ratio would be 3:1. For probability, divide the number of favorable outcomes by the total number of outcomes; for instance, if there are 4 squares and 2 represent a specific genotype, the probability is 2 out of 4, or 50%.