1. Multi-Trait Inheritance
Section 5.7

2. Multi-Trait Inheritance
Learning Goal: To learn how to predict the outcome of two traits being inherited at one time.
Success Criteria:
I know I am succeeding when I can…
explain that dihybrid crosses are used to determine the inheritance patterns of two pairs of alleles
explain Mendel’s law of independent assortment
predict the phenotypic ratio of dihybrid crosses

3. Multi-trait Inheritance
dihybrid cross: a cross that involves two genes at the same time (ex. seed color AND shape)
Recall …. the Law of Independent Assortment: if genes are located on separate chromosomes, they will be inherited independently of one another

4. Multi-trait Inheritance Cont’d…
Mendel crossed parent plants that were homozygous for seed shape and color (RRYY x rryy) to produce plants (the F1 generation) that were heterozygous for these two traits
He then used these F1 plants to perform a dihybrid cross

5. Multi-trait Inheritance Cont’d…
because each gene assorts independently of each other a heterozygous individual for two characteristics will produce four possible gametes
a parent that is RrYy can generate the possible gametes RY, Ry, rY, and ry

6. Multi-trait Inheritance Cont’d…
offspring characteristics were of every combination possible
9 round yellow seeds, 3 round green, 3 wrinkled yellow, and 1 wrinkled green
a dihybrid cross results in a phenotypic ratio of 9 : 3 : 3 : 1

7. Solving Dihybrid Problems
Step 1:
Determine the possible gametes from each parent.
Step 2.
Draw a Punnett square of the dihybrid cross (Write the possible gametes from one parent across the top and the possible gametes from the other parent down the left-hand side).
Step 3:
Execute the cross. (Pair up the alleles for the same gene.)
Step 4:
Find phenotypic ratio. (Start with number that will exhibit both dominant characteristics, followed by number that are dominant for only one of the characteristics, and then finally with number that are recessive for both characteristics.)

8. Solving Dihybrid Problems Cont’d…
Example #1: Determining Phenotypic Ratio In watermelons, the green colour gene (G) is dominant over the striped colour gene (g), and round shape (R) is dominant over long shape (r). A heterozygous round green colour (GgRr) watermelon plant is crossed with another heterozygous round green colour (GgRr) plant. Determine the expected phenotypic ratio of the F1 generation
Parent Genotype:
Possible Gametes:

9. Solving Dihybrid Problems Cont’d…
Example #2: Examining a Homozygous Cross Assume that in guinea pigs, black fur (B) is dominant over white fur (b), and a rough coat (R) is dominant over a smooth coat (r). If a black, rough-furred guinea pig that is homozygous dominant for both traits (BBRR) is crossed with a white, smooth-furred guinea pig (bbrr), what are the expected phenotypes in a large litter?
Parent #1 Genotype:
Possible Gametes:
Parent #2 Genotype:
Possible Gametes:

10. Practice Problem
In some breeds of dogs, a dominant allele controls the characteristic of barking (B) while on a scent trail. The allele for non-barking trailing dogs is (b). In these dogs an independent gene (E) produces erect ears and is dominant over drooping ears (e). For each of the following mating situations, calculate the phenotype ratio of the offspring:

11. Practice Problem Cont’d…
A non-barking trailer with erect ears (heterozygous) is mated with a heterozygous barking trailer with drooping ears (bbEe x Bbee).

12. Practice Problem Cont’d…
A non-barking trailer with drooping ears is mated with a heterozygous barking trailer with drooping ears (bbee x Bbee).

13. Practice Problem Cont’d…
A heterozygous barking trailer with heterozygous erect ears is mated with a heterozygous barking trailer with heterozygous erect ears (BbEe x BbEe).

14. Practice Problem Cont’d…
A heterozygous barking trailer with heterozygous erect ears is mated with a non-barking trailer with drooping ears (BbEe x bbee).

15. Multi-Trait Inheritance
Learning Goal: To learn how to predict the outcome of two traits being inherited at one time.
Success Criteria:
I know I am succeeding when I can…
explain that dihybrid crosses are used to determine the inheritance patterns of two pairs of alleles
explain Mendel’s law of independent assortment
predict the phenotypic ratio of dihybrid crosses

16. Homework
5.7 questions #1-4