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Multiple Alleles

Multiple Alleles. For each trait observed by Mendel…. Only 2 alleles existed (T & t, for example) Many traits are controlled by multiple alleles 2 examples include Eye color in Drosophila (fruit flies) Blood types in humans. Eye Color in Drosophila. 4 alleles control eye color

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Multiple Alleles

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  1. Multiple Alleles • For each trait observed by Mendel…. • Only 2 alleles existed (T & t, for example) • Many traits are controlled by multiple alleles • 2 examples include • Eye color in Drosophila (fruit flies) • Blood types in humans

  2. Eye Color in Drosophila • 4 alleles control eye color • E1 = Wild • E2 = Apricot • E3 = Honey • E4 = White • E1 > E2 > E3 > E4

  3. Normal Fruit Fly

  4. Mutant Fruit Flies Short winged fly Normal fruit fly Curly winged fly

  5. Eye Color in Drosophila • Phenotypes Genotypes • Wild Type E1E1, E1E2, E1E3, E1E4 • Apricot E2E2, E2E3, E2E4 • Honey E3E3, E3E4 • White E4E4

  6. Predict the phenotypic outcome if a honey colored heterozygous fly is crossed with a white fly! E4 E3 E3E4 E4E4 E4 E4 E3E4 E4E4 Genotypes 2 E3E4 : 2 E4E4 Phenotypes 2 Honey : 2 White

  7. What are the possible phenotypes of the parents in a cross which produces the following offspring? ? ? E1E2 E1E3 ? ? E2E3 E3E3 Genotpes E1E3 : E2E3 Phenotypes Wild & Apricot

  8. Another Example of Multiple Alleles Possible alleles C cch ch c

  9. Antigen type Determines Blood type Blood Types

  10. Person with blood type A Has antigen A on RBC’s & Antibody B (floating in plasma) A A A A A A A A A A

  11. Blood Typing in Humans • Another example of multiple alleles • Controlled by 3 alleles • IA, IB and i • IA and IB are said to be codominant • If a person inherits both of them, then antigen A and antigen B are on the RBC’s • i is recessive to IA and IB

  12. Blood Components Antigens A, B or Rh may be present on RBC surface

  13. Genotypes and Phenotypesfor ABO Blood Types • Genotype Phenotype Blood Type • IAIA, IAi A antigen A • IBIB, IBi B antigen B • IAIB A & B antigen AB • ii neither antigen 0

  14. Predict the phenotypic outcome if a person with blood type AB mates with a person with type O! IB IA IAi IBi i i IAi IBi Genotypes 2 IAi : 2 IBi Phenotypes 1 Type A : 1 Type B

  15. Blood Typing Problem 1 Mom Blood Type A Dad Unknown Blood Type Must carry IB__ IBIB IBi IAIB IAIA or IA i Baby Blood Type B IBIB or IBi

  16. Blood Typing Problem 1 Mom Blood Type B Dad Unknown Blood Type Must carry i__ IBi IAi ii IBIB or IB i Baby Blood Type O ii

  17. Punnet Squares for Codominance

  18. Calculate the probability of producing a son who is blood type A from the following cross! IB IA Must Use Product Rule Answer 0.5 X 0.5 = 0.25 or 25% IAi IBi i i IAi IBi Prob. Of producing Type A = 0.5 Probability of producing a son = 0.5

  19. Blood Typing and Gender • Calculate the probability of producing a daughter who is blood type A from a cross between a Type B mother and a Type A father, given that each of these individuals have a parent with Type O. • Since parents are ii, both must be carriers for i • Mother must be IBi, Father must be IAi

  20. Prob. of producing Type A = 0.25 • Prob. of producing a daughter = 0.50 • Therefore prob of producing Type A daughter must be found with the product rule…….. • 0.25 ( 0.5) = 0.125 or 1/8 or 13% • Diploma questions ask for answer rounded to 2 decimal places or to 2 significant digits

  21. Genetics Problem Set www.biology.arizona

  22. The Product Rule

  23. Incomplete Dominance Codominance Cattle Red X White = Roan Both genes expressed White and red hair present Intermediate Inheritance Snapdragons Red X White = Pink!! Blending occurs

  24. Red X White = Pink Gene for red (R) is incompletely dominant to gene for white (W)

  25. Incomplete Dominance: Blending/3 distinct phenotypes

  26. Predict the phenotypic outcome if a Red (RR) snapdragon is crossed with a White (WW) sd! R R Capital Letters used for both alleles since they are equally Dominant RW RW W W RW RW Genotypes All RW Phenotypes All pink!

  27. Predict the phenotypic outcome if a red (RR) snapdragon is crossed with a pink (RW) sd! R R RR RR R W RW RW Genotypes 2 RR : 2 RW Phenotypes 2 Red : 2 pink

  28. Intermediate? Or Co-dominant? Ask yourself does blending occur??

  29. Predict the genotypes of the parents! Rr & Rr

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