2. 4.4 - Dihybrid Crosses
Dealing with the mating of two individuals and tracking TWO traits or genes.

3. These type of crosses can be challenging to set up, and the square you create will be 4x4.

4. EXAMPLE
A pea plant that is heterozygous for round, yellow seeds is self fertilized, what are the phenotypic ratios of the resulting offspring? X

5. Step 1
Step 1: Determine the parental genotypes, the word "heterozygous" is the most important clue, and you would also need to understand that self fertilized means you just cross it with itself.
RrYy x RrYy

6. Step 2 Determine the gametes.
This might feel a little like the FOIL method you learned in math class. Combine the R's and Ys of each parent to represent sperm and egg. Do this for both parents.

7. Gametes after "FOIL"
RY Ry rY ry RY Ry rY ry

8. Step 3 Set up a large 4x4 Punnet square
Place one gamete set from the parent on the top, and the other on the side.

9. Step 4
Write the genotypes of the offspring in each box and determine how many of each phenotype you have.

11. In this case, you will have 9 round, yellow; 3 round, green; 3 wrinkled, yellow; and 1 wrinkled green

12. Example 2 – Guinea Pigs BB = black Bb = black bb = white
LL = short hair
Ll = short hair
ll = long hair

13. F2 = Genotype & Phenotype

17. Polygenic Inheritance
GENETIC COMPLEXIES
Polygenic Inheritance

18. POLYGENIC INHERITANCE
Polygenic inheritance is a fancy term for those genetic traits that are controlled by more than 1 gene.
Involves 2 or more genes influencing the expression of one trait.

19. With 2 or more allelic pairs found at different loci the number of possible genotypes is greatly increased.
Human eye color involves the interaction of 2 genes.
Human skin color involves the interaction of at least 3 genes.
Skin color variation can be modified by environmental factors.

22. Eye Color
There are at least 15 genes that have been determined to help regulate eye color.
There are 2 primary genes associated with eye color variation are OCA2 and HERC2, and both are localized on Chromosome 15.

26. SKIN COLOR
Skin Color is based on 3 main types of genes.