Constructing a Punnett square for a dihybrid cross (a cross following the inheritance of two traits) is similar to the method used for a monohybrid cross. Determine the alleles produced by each parent, draw the Punnett square, and then combine the gametes for each cell. The following web sites should help to demonstrate the process more clearly.
A helpful equation to use in solving genetics problems is to determine the number of different gamete types an individual can produce via meiosis. The equation is 2n = the # of different gamete types. In this equation, n is the number of heterozygous genes the individual has. For example, an individual of genotype AaBb can make 4 different gametes with respect to these two genes (gametes with genotype AB, Ab, aB, ab). An individual with genotype AABb only makes two different gamete types (AB and Ab).
Problem 1: Predicting gametes in a dihybrid cross - This tutorial teaches how to predict combinations of alleles in gametes of plants that are heterozygous for two traits. After viewing the tutorial, close the Dihybrid Cross window to return to this page. Provided by The Biology Project, from the University of Arizona.
Problem 3 : A genetic cross yielding a 9:3:3:1 ratio of offspring - This tutorial teaches how to set up a Punnett square for a dihybrid cross and how to interpret the results. After viewing the tutorial, close the Dihybrid Cross window to return to this page. Provided by The Biology Project, from the University of Arizona.
Problem 7 : Homozygous offspring of a dihybrid cross - Find the correct answer to the multiple-choice, dihybrid cross question. You will likely find it helpful to pull out a piece of paper and pencil in order to solve this problem. To view an explanation of the problem, select the "TUTORIAL" button. After viewing the correct answer, close the Dihybrid Cross Problem Set window to return to this page.
This animation (from Ricochet Science) explains how to create a Punnett square for a dihybrid cross:
To watch this video on YouTube (and see closed captioning) - press the arrow icon in the bottom right corner of the video player.