Genetic Crosses – 2 Traits


This worksheet was designed for freshman learning dihybrid crosses. Students struggle with setting up Punnet squares, so the squares are set up for them at first. Students only need to fill in the letters of the genotype can determine the phenotype proportions.

A final task requires students to set up their own 4×4 square when given the genotypes of the parents (GgBb x GgBb). I tell students to use the “FOIL” method to determine the alleles present in each sex cell.

This method shows students to recombine the letters so that there are four combinations to make a 4×4 square. These notes outline my method for teaching a dihybrid cross. I also have students use large whiteboards to practice setting up squares and counting the offspring phenotypes. Counting is often a challenge for students because they can’t read their own handwriting or choose letters that are difficult to distinguish (S vs s).

Students practice dihybrid crosses on whiteboards.

Grade Level: 8-12
Time Required: 15-20 minutes

HS-LS3-3 Apply concepts of statistics and probability to explain the variation and distribution of expressed traits in a population.