1. Genetic Analysis, Part 2 December 12, 2012 SBI 3U

2. Dominant vs. Recessive • Dominant trait-Strongest trait • Dominant trait-Masks or covers up the weaker trait • Which hair color do you think is dominant? • Which eye color do you think is dominant? • Which hair color do you think is recessive?

3. Common Misconception Recessive Traits are not rare traits. Dominant or recessive traits may be more common in a population. Example: Blonde hair is very common in parts of Scandinavia. Example: The trait of having six fingers on one hand is a dominant trait!

4. Questions to Think About Were traits that are dominant, actually dominant among our classmates? Is it possible to have traits that are not visible in your parents?

5. Test Cross Performed to determine the genotype of a dominant phenotype Always performed between the unknown genotype and a homozygous recessive genotype If any offspring show recessive trait – individual is heterozygous!

6. Example of Test Cross

7. Dihybrid Cross Inheritance of 2 separate traits Alleles assort independently – Law of Independent Assortment Ex: inheritance of the gene for colour (in pea plants) is not affected by either the wrinkled or round alleles

8. Law of Independent Assortment

9. Law of Independent Assortment Each of the pairs of genes determining a trait in the pea plant is located on each chromosome of a homologous pair Each gene is found at a specific place or locus

10. Dihybrid Cross