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Download Multiple Alleles and Polygenic Inheritance A. Multiple alleles
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1/13/09 Multiple Alleles and Polygenic Inheritance … a huge variety! A. Multiple alleles Genes having more than two alleles Note: this does not mean that an individual can have more than two alleles. (One from Mom, one from Dad.) It only means that more than two possible alleles exist in a population Example 1: Screech owl colors Example 2: Human blood type 1 1/13/09 Screech Owls A recent study suggests that in screech owls, red (R) is dominant to brown (R’), which is dominant to grey ( r ). Also abbreviated by: R > R’ > r Is it possible for a red owl and a brown owl to have a grey baby? Show with Punnett square(s), or explain in words. Solution Red: R R, RR’, Rr Brown: R’R’, R’r Grey: rr R’ r R RR’ Rr r R’r rr 2 1/13/09 ABO Blood Types Multiple alleles: IA, IB, and i (Note: IA and IB are codominant to each other, and i is recessive.) In 1943 a young woman, Joan Barry, sued Charlie Chaplin for parental support of her child. Charlie Chaplin's blood was type O. The mother of the child had type A and her baby girl had type B blood. Based on blood type, could the child have been Charlie Chaplin's? Show with Punnett square or explain in words. Solution Type O, Charie must have genotype ii. Why? Type A, the mother must have genotype IAi. Why? Type B, the baby must have genotype IBi. Why? So, baby had to get an “i” from mom (OK!), and an “IB” from dad (Uh Oh!) Charlie Chaplin could NOT have been the father. Charlie was found guilty and had to pay child support, because the blood test was inadmissible. 3 1/13/09 B. Polygenic Traits More than one gene contributes to the expression of the trait For example, skin color, hair color, eye color, height. Height is a polygenic trait Skin Color Up to 7 genes code for skin color. Here is an example of the possibilities with just 3 genes: AA = dark Aa = less dark aa - light And similarly for the other two genes - in all cases dominance is incomplete for each gene, each contributing a certain amount of melanin. Think of each “capital” allele (A, B, C) as adding a dose of brown paint to white paint. 4