In need of a giant dihybrid cross Punnett square? Search no more! Dihybrid cross calculator allows you to compute the probability of inheritance with two different traits and four alleles, all at once. It is a bigger version of our basic Punnett square calculator.
This two-trait Punnett square will allow you to calculate both the phenotypic and genotypic ratio of the dihybrid cross. It's also the perfect place to get some basic knowledge on the construction of genetic squares and learn some inheritance rules!
How to do a dihybrid cross?
4x4 Punnett squares might be quite a challenge! There's quite a lot to deal with:
- 16 sets of crosses in each try;
- 9 possible versions of genotype;
- 4 possible mother's alleles;
- 4 possible father's alleles; and
- 81 versions of the Punnett square!
If you want to save yourself a lot of time and hassle, we recommend you use our dihybrid cross calculator. If you're here for a challenge, follow our guidance below!
➡️ Say we'd like to know the chances that our baby will have curly and light-colored hair. The mother of a child is a blonde, with curly hair, while the father has light-colored, straight hair. (You may also start with something easier - like blood type inheritance!)
- What are the traits we're looking for? We got two different traits: the color of the hair, and the type of hair.
- trait A - color
- trait B - type
- What is the type of inheritance? Both traits are autosomal - located on chromosomes 1-22. To simplify things, we can assume that curly and dark-colored hair are dominant traits with single genes that control them.
- A - curly hair (dominant)
- a - straight hair (recessive)
- B - dark hair (dominant)
- b - light hair (recessive)
- What are the possible sets of alleles?
- The mother is heterozygous when it comes to curly hair (A, a), and homozygous recessive when it comes to hair color (b, b). Her possible combination of alleles are: Ab, ab
- The father is homozygous recessive in both traits (a, a, b, b), so he produces one combination of alleles: ab
Let's make the dihybrid cross worksheet! Remember, the size for the two-trait, dihybrid Punnet square must be 4x4!
Now, since you already know how to do Punnett squares with 2 traits, you're ready to interpret the results! You can find the dihybrid cross ratio in the section below.
Genotype and phenotype ratios
We will start with the genotypic ratio. We can either count the combinations in the Punnett square, or use the dihybrid cross calculator to compute it for us. In the example presented to us in the section above the task is really easy: 50% of the Punnet square is taken by the Aabb combination, and the other half is aabb. It's easy to calculate that the genotypic ratio is 0.5:0.5, which is equal to 1:1.
What is the phenotypic ratio?
- Phenotype for Aabb = Ab
- Phenotype for aabb = ab Now we know that that the phenotypic ratio is equal to the genotypic ratio = 1:1.
In conclusion, 50% of the couple's children will be born with alleles Ab - that is curly, blond hair. The other half will be born with alleles ab - they will inherit straight, blond hair. 👱♀️👱
Our dihybrid cross calculator will provide you with the percentages for the different sets of alleles. To receive the genotypic ratio, you need to divide all those numbers by the smallest percentage received, which gives you the lowest possible integer. Look at the example below:
- 6.25 : 12.5 : 6.25 : 12.5 : 25 : 12.5 : 6.25 : 12.5 : 6.25
6.25 is the smallest number, so we need to divide everything by 6.25:
- 1 : 2 : 1 : 2 : 4 : 2 : 1 : 2 : 1
Voila! Your genotypic ratio is ready.
If you need any help with those calculations, check out our Greatest Common Factor tool!