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

Demonstrate ability when completing genetics problems

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?