Dihybrid Crosses Genetics

Dihybrid cross- 2 different genes affecting 2 different traits. *the different genes must be on different chromosomes. *How many possible phenotypes in a dihybrid cross? ______ *To determine the number of different gametes that result- 2n power. This is because of metaphase I of meiosis and the way the chromosomes line up on the metaphase plate.(next slide)

The slide shows the different way of how two homologs can line up on the metaphase plate to form 4 different gametes.

Mendel's 2nd law of independent assortment.- In heterozygotes, if two different genes are on two different chromosomes, they will assort independent of one another in the formation of gametes.

How to determine gamete formation (use the foil method, 1st and 3rd letter, 1st and 4th letter, 2nd and 3rd letter, 2nd and 4th letter)

How to do a dihybrid cross: Setting up a Punnett square How many different types of gametes are produced by each parent? (use the foil method) Place the gametes on the Punnett square. Determine the genotypes of the offspring within the Punnett square. What is the phenotypic ratio of the cross?

Cross GgTt x GgTt

Results: Check your work!

Lets determine the genotypes:

Genotypes cont’d

What are the genotypes of the parents below?