In this video, we're going to talk directly about dihybrid crosses and their Punnett squares. A dihybrid cross is really just cross-fertilization between two dihybrid organisms. Recall from our previous lesson video that dihybrid organisms are organisms that are heterozygous for two specific genes. There is a very characteristic phenotypic ratio for dihybrid crosses that you should all be familiar with. That characteristic phenotypic ratio is 93 31. We'll be able to get some clarity on that once we get to our image down below.
Take a look at this image over here—a dihybrid cross crossing two dihybrid organisms. Notice that parent number 1 is a dihybrid organism because it's heterozygous for two genes: the shape and color genes. Parent number 2 is also dihybrid in the same way because it's heterozygous for these two genes. Dihybrid organisms have more possibilities when it comes to their gametes. They have more gametes than what we've seen before in our other Punnett squares. These increased possibilities of gametes create a larger, more complex Punnett Square, but it works in the same way as our previous Punnett squares, where each box represents a possible fertilization event of the gametes that you see aligned.
When we examine the results of this dihybrid cross Punnett square, you'll see a very characteristic phenotypic ratio where there are 9 possibilities that have the dominant trait for both genes. So 9 round and yellow phenotypes—dominant-dominant phenotypes. Then we have 3 dominant recessive phenotypes—3 round green phenotypes. There are another 3 that are recessive dominant, so 3 wrinkled yellow phenotypes, and then one that is recessive, recessive— one wrinkled green phenotype. This 93 31 phenotypic ratio is very characteristic of a dihybrid cross, and it's evidence to show that independent assortment occurs.
This concludes our introduction to dihybrid crosses and their Punnett squares and how they create this characteristic phenotypic ratio of 93 31. We'll be able to apply the concepts that we've learned here as we move forward in our course. So, I'll see you all in our next video.