TYPES OF DOMINANCE
INCOMPLETE DOMINANCE
• A form of intermediate(in-between) inheritance in
which one allele for a specific trait is not completely
expressed over its paired allele. This results in a third
phenotype in which the expressed physical trait is a
combination (blending) of the phenotypes of both
alleles.
INCOMPLETE DOMINANCE
Alleles are still inherited according to Mendel's basic rules, even when they show
incomplete dominance.
YOU TRY IT
a.
b.
c.
d.
In snapdragons, flower color is controlled by incomplete dominance.
The two alleles are: RED=R White=W
The heterozygous genotype is expressed as pink.
What is the phenotype of a plant with the genotype RR? ___________
What is the phenotype of a plant with the genotype WW? ___________
What is the phenotype of a plant with the genotype RW? ___________
A pink-flowered plant is crossed with a white-flowered plant. What is the probability of
producing a pink-flowered plant? ____% Draw the Punnett square.
e. Show the genotypes of the parents: ____ X ____
f. What cross will produce the most pink-flowered plants? Show a punnett square to
support your answer. Parents: ____ X ____
CODOMINANCE
With codominance BOTH alleles are expressed.
RR=Red BB=Blue BR=spotted
Can YOU draw the Punnett Square?
INCOMPLETE DOMINANCE VS
CODOMINANCE
Incomplete dominance BLENDS alleles
Codominance show BOTH alleles
INCOMPLETE OR CODOMINANCE?
INCOMPLETE OR CODOMINANCE?
BLOOD TYPES
• Human blood type is determined by codominant
alleles.
• There are 3 different alleles for human blood type: A,
B, and O.
• We all have 2 alleles for blood type – one from our
biological mother and one from our biological father.
• There are 6 possible genotypes for blood type.
• American Red Cross:
http://www.redcrossblood.org/learn-aboutblood/blood-types
• http://www.redcrossblood.org/learn-about-blood/bloodfacts-and-statistics