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Co-dominance & Incomplete Dominance Notes

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Co-dominance Co-dominance when both alleles of a gene contribute to the phenotype Examples: Chickens black feathers is co- dominant with white feathers, so heterozygous chickens show up with speckled black and white feathers Human Blood Types

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Human Blood Types are another example of co- dominance There are 3 alleles for this gene (I A, I B & i) and i is recessive, while I A and I B are co-dominant, so people who receive one of each of these alleles will have AB blood IAIAIAiIAIAIAi IBIBIBiIBIBIBi IAIBIAIB

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Co-Dominance Sample Problems #1 Use the chart to answer the following questions: Write the genotype for each person based on the description: Homozygous for the B allele I B I B Heterozygous for the A allele I A i Type O ii Type AB I A I B

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Co-Dominance Sample Problem #2 Pretend that Brad Pitt is homozygous for the type B allele, and Angelina Jolie is type O. Do a Punnett square to determine all the possible blood types of their baby. All their offspring, will be I B i, so will have Type B blood i ii i I B I B IBiIBi IBiIBi IBiIBiIBiIBi

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Co-Dominance Sample Problem #3 Two parents think their baby was switched at the hospital. The mother has blood type A, the father has blood type B, and the baby has blood type AB. Mothers genotype I A I A or I A i Fathers genotype I B I B or I B i Babys genotype I A I B Do a Punnett square that shows the babys genotype as a possibility Was the baby switched? NO IB iIB i I A i IAIBIAIB IBiIBi iiIAiIAi

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Co-Dominance Sample Problem #4 Based on the information in this table, which man could not be the father of the baby? Justify your answer with a Punnett square. Sammy the player NameBlood Type MotherType A (Heterozygous) BabyType B Sammy the playerType O George the sleezeType AB The waiterType AB The cable guyType B i ii i I A i IAiIAi ii IAiIAi

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Probability What is probability? The likelihood a particular event will occur How is it used in Biology? Used to predict phenotypes and genotypes of offspring (diseases & disorders for people planning families)

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Additional Information Probability = # of times an event occurs # of trials A previous event does not affect future outcomes. Each event is separate and independent Ex. Gender of baby 50/50 chance of each sex each birth

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Incomplete Dominance Incomplete Dominance when one allele is not completely dominant over the other allele, so it produces offspring with a third phenotype that is a blending of the parental traits. It's like mixing paints, red + white will make pink. Red doesn't totally block (dominate) the white, instead there is incomplete dominance, and we end up with something in-between. Instead of using a capital letter for the dominant trait & a lowercase letter for the recessive trait, the letters we use are both going to be capital (because neither trait dominates the other).

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Incomplete Dominance Four oclock flowers show this type of inheritance Red flowers are RR, white are WW and the heterozygous genotype RW, gets you pink flowers So looking at the following Punnett Square, what percentage of pink flowers would be produced? 100%

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Incomplete Dominance Sample Problem #1 Suppose you cross 2 pink flowers that show incomplete dominance (R=Red, W=W). What are the parent genotypes? RW; RW Do a Punnett Square. What is the probability of: Red 25% White 25% Pink 50% R WR W R W RR RW WW

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Incomplete Dominance Sample Problem #2 In Elmos family red (R) and blue (B) show incomplete dominance. What is the Genotype of: Red RR Blue BB Purple RB

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Incomplete Dominance Sample Problem #3 If both of Elmos parents were purple, what is the probability that his next sibling will be blue (Do a Punnett square to show your results)? 25% R BR B R B RR RB BB