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 Beyond Dominant & Recessive Alleles Incomplete Dominance & Codominance.

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Presentation on theme: " Beyond Dominant & Recessive Alleles Incomplete Dominance & Codominance."— Presentation transcript:

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).

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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.

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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 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!!!

16 Let’s 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

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


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