1. Or what happens when you look at 2 traits at the same time
Dihybrid crosses
Or what happens when you look at 2 traits at the same time

2. Patterns of inheritance
Monohybrid crosses. Looks at one (1) trait with 2 phenotypes
Simple dominance characteristic phenotypic ratio 3:1
Test cross crosses unknown dominant phenotype with the homozygous recessive.
If F1 has a 1:1 dominant to recessive ratio, then parent is heterozygous
If the F1 is 100% dominant, then the parent was homozygous.
Codominance both traits are expressed equally in the F1 heterozygote.
RR = red WW = white RW = red and white stripes
characteristic phenotypic ration 1:2:1 with 3 phenotypes
Incomplete dominance the traits are blended in the F1 heterozygote.
RR = red WW= White RW = pink

3. Dihybrid crosses crossing two (2) traits with 2 phenotypes each at the same time
Kristina and Jessica decided to breed peas like Mendel for next years science fair. In their flowers single flower was Dominant (F) and double flower was recessive (f) . In the height trait tall is dominant(H) and short is recessive (h). The Genotype always has 4 letter 2 of each phenotypes
What is the genotype of a parent that is heterozygous for both traits?
Ff Hh
What is the genotype of a parent that is homozygous dominant for height and heterozygous for flowers?
Ff HH
What is the genotype of the parents if they were pure for both recessive traits?
ff hh

4. How do you make the gametes?
This is the tricky part. Each parent has 2 of each trait.
Each gamete has one of each trait.
Parent Heterozygous for both traits Ff Hh
There are 4 possible gametes.
FH Fh fH fh
Parent homozygous for 1 trait and heterozygous for the other. FF Hh
There are only two different gametes.
FH FH Fh Fh

5. This is Mendel’s Law of Independent Assortment
If you cross two traits at the same time they assort themselves independently
The inheritance of one trait has no effect on the inheritance of the other trait.
Just because it’s tall doesn’t determine if it’s double or single.

6. What is the phenotypic ratio when we cross 2 peas that are heterozygous for each trait.
Given: FfHh x FfHh
Punnett square: because you have 4 possible gametes your Punnett has to be 4 x 4.
Gametes FH Fh fH fh FH Fh fH fh

7. How do you find the phenotypic ratio?
Gametes FH Fh fH fh FH
Fh FFHh FFhh Ff Hh Ffhh
fH FfHH FfHh ffHH ffHh
fh FfHh Ffhh ffHh ffhh
There are 4 Phenotypes single tall single short double tall double short
The phenotypic ratio is : : :
FfHh
FFHH
FFHh
FfHH

8. You try this one. A pea homozygous dominant for height and heterozygous for flowers is crossed with a pea that is heterozygous for height and homozygous recessive for flowers
Parents cross Ff HH x ffHh
Possible gametes
FH fH fH fh
Punnett square
Because each parent has only two gametes then the Punnett only has to have 4 squares

9. What is the phenotypic ratio of the F1
Gametes F1
Phenotypic ratio of F1 is :
Single tall : double tall
: 2 FH fH fH
ffHH
FfHH fh
FfHh
ffHh