1. Dihybrid Cross & Beyond Dominant and Recessive Genetics
January 6, 2011

2. Warmup
In ginuea pigs, short hair (S) is dominant to long hair (s). Two short-haired ginuea pigs breed and one of the resulting offspring is long-haired.
Draw the punnett square to represent this situation
What are the genotypes of the parents?

3. Law of Independent Assortment
Mendel wondered if alleles were “linked” together.
He knew yellow seeds (Y) were dominant over green (y), and round seeds (R) were dominant over wrinkled (r). But…
Are all yellow seeds were round?
And all green seed were wrinkled?

4. Independent Assortment cont.
So he crossed them- Got the F1
RRYY (round yellow) x rryy (wrinkled green)
rryy
RRYY
 ry ry
 RY
 RrYy
  RrYy

5. Independent Assortment cont
Then he did the F2
He crossed the RrYy with RrYy
Since the seeds in the generation no longer linked being yellow and round and green and wrinkled. Mendel now new that genes were independent of each other

6. Two laws from his observations
Law of Segregation- when you make your gametes (sex cells), the copies of a gene separate.
Ex. One of your sex cells may have an allele for brown hair and another gamete may have an allele for red hair
Law of Independent Assortment- genes for different traits separate independently of one another
Contributes to genetic variations observed in plants and animals

7. Beyond Dominant and Recessive
Some alleles are not dominant or recessive and others are not controlled by just one gene!
Incomplete Dominance
Codominance
Multiple Alleles
Polygenic traits

8. Incomplete Dominance When one allele is not dominant over another.
The heterozygous genotype produces a mix of the phenotypes
Red and white flower producing PINK

9. Codominance When both alleles contribute to the phenotype
Not mixed, but both present
Example: Red cows x White cows  red and white spotted cows

10. Multiple Alleles When a gene has more than 2 possible alleles
Although individuals can only have 2 there are more in nature
Example – ABO Human Blood Type
Example– Fur color in rabbits
Single gene, 4 alleles

11. Blood Types

12. Polygenic trait
When trait/phenotype is controlled by the interaction of more than 1 gene
Example: Skin color in humans, high blood pressure and height
Skin color- more than four different genes that control this trait

13. Polygenic traits- Skin Color

14. Homework Finish green “Genetic Basics” worksheet
# 15, 16, 17, 20
Fill in front side of 11-3 notes sheet (read the section to complete)
Quiz tomorrow!