beyond dominant & recessive alleles
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Beyond Dominant & Recessive Alleles. Incomplete Dominance & Codominance. Learning Goals. 1. Describe incomplete dominance. Describe c odominance . 2. Compare and contrast incomplete dominance and codominance . Give 2 similarities and 1 difference. - PowerPoint PPT PresentationTRANSCRIPT
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Beyond Dominant & Recessive Alleles
Incomplete Dominance & Codominance
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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.
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Beyond Dominant and Recessive Alleles
Some alleles are neither dominant nor recessive, and many traits are controlled by multiple alleles or multiple genes.
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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
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Example: A cross between red (RR) and white (WW) snapdragons produces pink flowers (RW).
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Homozygous
RR(Red)
HeterozygousRW
(Pink)
HomozygousWW
(White)
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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
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Example: A cross between black (BB) and white (WW) chickens produces chickens speckled with black and white feathers (BW).
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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.
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•Example: A human’s blood type is determined by a single gene that has three different alleles.
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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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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.
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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!!!
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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
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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
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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
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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
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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
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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