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Codominance and Multiple Allele Notes

Codominance and Multiple Allele Notes. January 12, 2012. I. What is codominance?. Some traits do not have a clear dominant & recessive allele. In this case, BOTH alleles are expressed. Example: Red flowers and White flowers would produce R e d & W h i t e s p o t t e d flowers

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Codominance and Multiple Allele Notes

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  1. Codominance and Multiple Allele Notes January 12, 2012

  2. I. What is codominance? • Some traits do not have a clear dominant & recessive allele. • In this case, BOTH alleles are expressed. • Example: Red flowers and White flowers would produce Red & White spotted flowers • This is called codominance because BOTH alleles act like they’re dominant.

  3. Example #1 • Cattle have red, roan, & white coat colors. Roan is a “mixture” of the genes for red & white. • There are three possible expressions of this trait… what would the genotypes be? RR White Cow: WW Red Cattle: Roan bull: RW

  4. A roan bull is mated with a white cow. What are the genotypes of the parents? P1=___________ P2=__________ • What is the phenotypic ratio for the F1 generation? RW WW R W W RW WW RW W WW

  5. Example #2 • A red bull mated with a white cow produces a roan calf. • What are the genotypes of the bull, cow and calf? Bull_____ Cow_____ Calf_____ RR WW RW

  6. What would be the probability of having a RED calf if the two were mated again? 0%

  7. II. What are multiple alleles? • Sometimes there are more than two alleles possible for a trait. • However, each individual organism will still only have two alleles (one from Mom and one from Dad) even if there are more • Examples: blood types, hair color, and eye color • This can lead to more possible genotypic and phenotypic ratios

  8. C. Blood Types • Human blood type is a good example of BOTH multiple alleles and codominance. • There are 3 possible alleles & two of them act dominant(A and B are dominant while o is a recessive allele) • Blood Type Alleles • Type A: causes cells to make protein A for the surface of the RBC’s • Type B: causes cells to make protein B for the surface of the RBC’s • Type O: causes cells to make no proteins for the surface of the RBC’s

  9. Both A and B alleles are DOMINANT over the O allele because if any A or B allele is present, they will be expressed and the A or B proteins will be made

  10. A B (RBC) (RBC) A B A B A B A B • Label the possible genotypes of the following three phenotypes: (RBC) Phenotype: Genotype: A B O BB, BO OO AA, AO

  11. Example #1 • Suppose a child is of blood group B and its mother is of blood group O. • To what genotypic groups may the father have belonged? • The child? • The mother? AB, BB, BO BO OO

  12. Example #2 • A child has blood group AB. What 4 PHENOTYPIC blood type combinations could its parents have? 1. Blood type______ x Blood type_____ 2. Blood type______ x Blood type______ 3. Blood type______ x Blood type______ 4. Blood type______ x Blood type______ A B A AB AB B AB AB

  13. Example #3 • A man has blood type A and his wife has blood type B. A child is born with blood type O. The man accuses his wife of infidelity saying that this child could not possibly he his. Do you agree or disagree? Explain why. Disagree both could be AO and BO, so therefore both O alleles could be given to child

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