Incomplete Dominance and
Codominant Traits
Incomplete Dominance
(think pink flower)
• The heterozygous offspring
genotype has a phenotype color
that is in-between the parent’s
color
• There is no clear dominant trait
–Ratio 1:2:1
• “Mixture” or “intermediate” color of
the parents
Codominance
(think checkered-chicken)
• Codominance
– 2 dominant alleles are both
expressed equally at the same
time for the same trait
Sickle-Cell Anemia
A Codominant Trait
• High prevalence in African-Americans
that are heterozygous for sickle cell
• Sickle cell protects against malaria
• Sickle-cell anemia means people
make both regular hemoglobin and
“sickled” hemoglobin
–Sickled hemoglobin cannot carry oxygen
very well.
Sickle Celled Hemoglobin vs.
Regular Hemoglobin