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Incomplete dominance Codominance Multiple alleles

Incomplete dominance Codominance Multiple alleles. Ch. 10.3 (p. 215-216). Incomplete dominance. This is a case where neither of the 2 alleles is totally dominant over the other So instead of having 2 phenotypes…we see an appearance of a 3 rd phenotype

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Incomplete dominance Codominance Multiple alleles

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  1. Incomplete dominanceCodominanceMultiple alleles Ch. 10.3 (p. 215-216)

  2. Incomplete dominance • This is a case where neither of the 2 alleles is totally dominant over the other • So instead of having 2 phenotypes…we see an appearance of a 3rd phenotype • In dominant/recessive cases, AA and Aa showed the dominant phenotype • In incomplete dominance, Aa will show an intermediate of the other 2 phenotypes

  3. Example of incomplete dominance • Snapdragons Red x White (P1) All Pink (F1)

  4. Example con’t • All F1 offspring were heterozygous • Let’s take 2 F1 individuals to make an F2 generation Pink x Pink Red, Pink, and White

  5. Using alleles (letters) for incomplete dominance • Since there isn’t a recessive gene here, we WILLNOT use a lower case letter • Instead we use… R = Red R’ = White • So our possible genotypes and phenotypes are: RR = Red RR’ = Pink R’R’ = White

  6. RR x R’R’ (P1) All R R’ (F1) RR’ x RR’ 1RR: 2RR’: 1R’R’ *Also our phenotypic ratio is: 1 Red: 2 Pink: 1 White The example written in alleles (letters)

  7. Codominance • This is a case where neither of the 2 alleles is totally dominant over the other, but we can still see each phenotype product individually (they’re not blended) • So again, we’ll see 3 phenotypes instead of 2…the heterozygous will show a combination of the other 2

  8. Example of codominance • Chickens with checkered feathers: Black x White(P1) All checkered (F1) Written in alleles as: BB x B’B’(P1) All BB’ (F1)

  9. Example con’t • Taking it to the F2: BB’ x BB’ 1BB: 2BB’: 1B’B’ Phenotypic ratio: 1 Black: 2 Checkered: 1White

  10. Multiple Alleles • For some traits, more than 2 alleles exist in the population (each individual still only has 2 alleles for that trait) • Having more than 2 alleles increases the possible genotypes and phenotypes for the trait

  11. Example of multiple alleles • Blood type for humans • 3 alleles: IA = A IB = B i = O • IA and IB are codominant to each other • IA and IB are both dominant over i

  12. Blood Types

  13. Example multiple allele problem • A person homozygous for Type A marries a person with Type O. What are the possible outcomes of bloodtypes for their children?

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