7.2 Dominance & Blood Type

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

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

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

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

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

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

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

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

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

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?