Beyond Dominant & Recessive Alleles

1. Beyond Dominant & Recessive Alleles Incomplete Dominance & Codominance

2. Learning Goals • 1. Describe incomplete dominance. Describe codominance. • 2. Compare and contrast incomplete dominance and codominance. Give 2 similarities and 1 difference. • 3. Explain how letters are chosen when doing punnett square problems for incomplete dominant and codominant traits • 4. Explain what multiple alleles are and give an example • 5. Describe what a polygenic trait is and give an example.

3. Beyond Dominant and Recessive Alleles • Some alleles are neither dominant nor recessive, and many traits are controlled by multiple alleles or multiple genes.

4. Incomplete Dominance  • Incomplete dominance - when one allele is not completely dominant over another. • Heterozygous genotype = BLEND • Since one allele is not completely dominant over the other allele, we use two different capital letters to represent the alleles

5. Example: A cross between red (RR) and white (WW) snapdragons produces pink flowers (RW).

6. Homozygous RR (Red) Heterozygous RW (Pink) Homozygous WW (White)

7. Codominance  • Codominance - both alleles contribute to the phenotype. • Heterozygous genotype = both traits appear • Since one allele is not completely dominant over the other allele, and both traits appear together, we use two different capital letters to represent the alleles

8. Example: A cross between black (BB) and white (WW) chickens produces chickens speckled with black and white feathers (BW).

10. Multiple Alleles  • Multiple alleles -genes that are controlled by more than two alleles. • An individual can’t have more than two alleles (Remember you get one copy from each parent). However, more than two possible alleles can exist in a population.

11. Example: A human’s blood type is determined by a single gene that has three different alleles.

12. Polygenic Traits • Polygenic traits -traits controlled by two or more genes. • Skin color in humans is a polygenic trait controlled by more than four different genes.

14. Learning Goals • 1. Describe incomplete dominance. Describe Codominance. • 2. Compare and contrast incomplete dominance and codominance. Give 2 similarities and 1 differences • 3. Explain how letters are chosen when doing punnett square problems for incomplete dominant and codominant traits • 4. Explain what multiple alleles are and give an example • 5. Describe what a polygenic trait is and give an example.

15. Whiteboard Practice • Step 1: Incomplete Dominance or Codominance?????? • Step 2: You will be given the 3 phenotypes, Write the corresponding genotypes. • 2 alleles (1 from mom, 1 from dad) • Use the 1st letter for each trait • Both letters are capitol • Step 3: Set up and fill-in a punnett square. Calculate percent probability for ALL 3 TRAITS!!!

16. Let’s do the 1st one together  • Birds can be blue, white, or white with blue-tipped feathers • 1. Incomplete Dominance or Codominance? • 2. Genotypes: blue- white – blue-tipped – 3. Show a cross between a white and blue-tipped bird

17. Practice Identifying • A cat can be black, tan, or tabby (black & tan) • 1. Incomplete Dominance or Codominance? • 2. Genotypes: black- tan – tabby – 3. Show a cross between a heterozygous tabby and tan cat

18. Practice Identifying • A Who can have curly hair, spiked hair, or wavy • 1. Incomplete Dominance or Codominance? • 2. Genotypes: curly- spiked – wavy- 3. Show a cross between a curly and wavy Who

19. Practice Identifying • A sneech can be tall, short, or medium • 1. Incomplete Dominance or Codominance? • 2. Genotypes: tall- short – medium – 3. Show a cross between two heterozygous sneeches

20. Practice Identifying • A horse can be black, white, or roan (black & white) • 1. Incomplete Dominance or Codominance? • 2. Genotypes: black – white – roan - 3. Show a cross between a heterozygous roan and black horse

21. Practice Identifying • Flowers can be white, pink, or red • 1. Incomplete Dominance or Codominance? • 2. Genotypes: white- pink – red- 3. Show a cross between a white and red flower