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Beyond Dominant & Recessive Alleles Incomplete Dominance & Codominance Slide 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. Slide 3 Beyond Dominant and Recessive Alleles Some alleles are neither dominant nor recessive, and many traits are controlled by multiple alleles or multiple genes. Slide 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 Slide 5 Example: A cross between red ( RR ) and white ( WW ) snapdragons produces pink flowers ( RW ). Slide 6 Homozygous RR (Red) Heterozygous RW (Pink) Homozygous WW (White) Slide 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 Slide 8 Example: A cross between black (BB) and white ( WW ) chickens produces chickens speckled with black and white feathers (BW). Slide 9 Slide 10 Multiple Alleles Multiple alleles -genes that are controlled by more than two alleles. An individual cant have more than two alleles (Remember you get one copy from each parent). However, more than two possible alleles can exist in a population. Slide 11 Example: A humans blood type is determined by a single gene that has three different alleles. Slide 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. Slide 13 Slide 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. Slide 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 1 st 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!!! Slide 16 Lets do the 1 st 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 Slide 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 Slide 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 Slide 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 Slide 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 Slide 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