1. 7.2 Dominance & Blood Type

2. Lesson Objectives Students will be able to:
Explain the difference between complete dominance, incomplete dominance and codominance
Demonstrate ability when completing genetics problems
Give the genotype of the ABO blood types

3. Dominance Alleles of different genes have different relationships
What we’ve seen before…
A “dominates” a
AA has same phenotype as Aa

4. Complete Dominance One trait is completely dominant over another
Dominant allele is completely dominant over recessive allele
RR and Rr have the same phenotype
R=red, r=white RR Rr rr

5. Incomplete Dominance Heterozygotes have an intermediate phenotype
Mixture of dominant and recessive phenotype
Different notation for alleles:
Same letter, but subscripts identify alleles
R1=red, R2=white
R1R1 = red
R2R2= white
R1R2 = pink

6. Codominance
Both phenotypes are equally represented in the heterozygote
Notation change:
Same letter, but subscripts identify alleles

7. Codominance Example: Flower color Base letter: F (flower)
F1 = red
F2 = white
Genotypes & Phenotypes:
F1F1 = red
F2F2 = white
F1F2 = red and white

8. Multiple Alleles Each individual can only have two alleles per gene
Because two homologous chromosomes
Some genes have more than two possible alleles
Three or more possible phenotypes

9. Multiple Alleles – Blood Type
Red blood cells have proteins on their surface
Alleles: IA, IB and i
IA allele: A protein on RBC surface
IB allele: B protein on RBC surface
i allele: no proteins on RBC
IA and IB are codominant
Both completely dominant to i

10. Multiple Alleles – Blood Type
Possible genotypes & phenotypes:
A blood type - IAIA
A blood type - IAi
B blood type - IBIB
B blood type - IBi
AB blood type – IAIB
O blood type - ii

11. Multiple Allele Problems
Wife with O blood and husband with AB blood; what are possible genotypes of children?
Father = A blood, mother = B blood, one child has O blood, what are the parents’ genotypes?