1. Dihybrid Crosses and Pedigrees

2. Dihybrid Crosses
Monohybrid punnett squares only look at one trait at a time (just flower color, just height…)
Law of Independent Assortment – most traits (found on different chromosomes) are inherited separately. Ex - Height does not have an impact on flower color. (See exception)
If you want to know the likelihood of inheriting two separate traits together (e.g. What are the chances of creating a plant that is tall AND has purple flowers?) you must use a dihybrid cross.
Note: dihybrid crosses will ONLY be done for regular Mendelian traits!

3. How to do a dihybrid cross
Step One – establish the genotypes of the parents.
Cross two pea plants that are heterozygous for both tall height and yellow flower traits.
Parent Genotypes: TtYy x TtYy
Step Two - Use the FOIL method to show the possible allele combinations each parent could pass on to their offspring.
FOIL = First alleles in a pair, Outside alleles in a pair, Inside alleles in a pair, Last alleles in a pair
Allele possibilities: TY, Ty, tY, ty
Step Three - Fill in the square to show the possible genotypes of the offspring. Keep the like letters together!

4. Dihybrid cross TY Ty tY ty
____ : ____ : ____ : ____

5. Dihybrid cross TY Ty tY ty TTYY TTYy TtYY TtYy TTyy Ttyy ttYY ttYy
____ : ____ : ____ : ____

6. Pedigrees

7. What is a pedigree?
Pedigrees are used to track how a trait transfers through multiple generations.

8. Pedigree Keys (See White Board)

9. Example Add numbers to the pedigree. How many generations?
How many kids did the parents in generation I have?
Were any of these kids affected? If so, which one(s)?
How many kids did the parents in generation II have?

10. The Blue People of Troublesome Creek

11. Fugate Pedigree