1. Multi-Trait Inheritance
Learning Goal: To learn how to predict the outcome two trait 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
Why do we resemble our parents? (We resemble our parents because we inherit traits from them.) 2. Why does asexual reproduction result in genetic clones? (During asexual reproduction, the organism makes a copy of itself without combining its genes with those from another organism. The offspring are a genetic copy of the single parent.) 3. Why are the offspring of sexual reproduction not genetically identical to either parent? (During sexual reproduction, genes from two individuals combine to produce offspring with new combinations of genes.)

2. 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
Mendel’s experiments consisted of many crosses. As a result of these experiments, he developed a way of mathematically
predicting the proportions of phenotypes in the off spring.

3. 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
In the following tutorial, you will learn how to set up Punnett squares, execute crosses, and interpret the results.

4. 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
In the following tutorial, you will learn how to set up Punnett squares, execute crosses, and interpret the results.

5. 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
In the following tutorial, you will learn how to set up Punnett squares, execute crosses, and interpret the results.

6. 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 ration. (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.)
In the following tutorial, you will learn how to set up Punnett squares, execute crosses, and interpret the results.

7. 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
Step 1: Write the symbols for the gametes across the top and along the left side of the square (Figure 8). Note that each parent can supply two possible gametes, each
containing one of two possible alleles.
Fill in the boxes of the Punnett square by combining the
gametes corresponding to each row and column.
Each box represents a possible offspring genotype.

8. 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?
Step 1: Write the symbols for the gametes across the top and along the left side of the square (Figure 8). Note that each parent can supply two possible gametes, each
containing one of two possible alleles.
Fill in the boxes of the Punnett square by combining the
gametes corresponding to each row and column.
Each box represents a possible offspring genotype.

9. 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:
In the following tutorial, you will learn how to set up Punnett squares, execute crosses, and interpret the results.

10. 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).
In the following tutorial, you will learn how to set up Punnett squares, execute crosses, and interpret the results.

11. Practice Problem Cont’d…
A non-barking trailer with drooping ears is mated with a heterozygous barking trailer with drooping ears (bbee x Bbee).
In the following tutorial, you will learn how to set up Punnett squares, execute crosses, and interpret the results.

12. 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).
In the following tutorial, you will learn how to set up Punnett squares, execute crosses, and interpret the results.

13. 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).
In the following tutorial, you will learn how to set up Punnett squares, execute crosses, and interpret the results.

14. Homework
5.7 questions #1-4