Download Incomplete Dominance

Codominance
• Defined: when a single gene
has more than one dominant
allele
• Ex: Cattle Coat
Red cow x White bull =
– Myth: Colors blend
– Reality: Both colors are equally
seen
• Ex: Human Blood types
Type A x Type B = Type AB
Blood Types
• Human blood type
has 3 alleles
– Dominant A allele
– Dominant B allele
– Recessive O
allele
• Type A & Type B
are dominant to type
O
• Type A and Type B
are codominant to
each other
Dad will pass 1 of these 3
Mom will
pass 1 of
these 3
Type A
Type AB
Type A
Child genotypes
Type B
Type B
Type AB
Type A
Type B
Type O
1 minute: Discuss with your neighbor.
Mike is heterozygous for type A blood and Lisa is
heterozygous for type B blood.
• A) Probability of child having
type A blood?
25%
• B) Probability of child having
codominant blood?
25%
• C) Probability of child being
Heterozygous?
75%
1 minute: Discuss with your neighbor.
Jason is homozygous for type A blood and Maria
who is heterozygous for type B blood. Their child,
Rick, has codominant blood.
Type A
Type B
a) Draw a pedigree for
this family.
b) Complete a Punnett
square for Jason and
Maria.
c) What were the odds
of Rick having
codominant blood?
50%
Maria BB
Bo
AA Jason
Ao
Rick
Codominant?
AB
Incomplete Dominance
PP
•
•
•
•
pp
pp
Defined: Neither allele is completely dominant
Heterozygous = blended appearance
More than 2 different phenotypes can occur
Ex: Many flower colors
In certain species of fish, blue scales (BB) and
yellow (YY) scales are incompletely dominant. Fill
in the Punnett square with the genotype of a blue
male and a green female.
A)
What is the probability
of obtaining
heterozygous fish?
50%
B)
Yellow fish?
0%
Carnations show incomplete dominance where a red allele and white
allele blend to make pink. A pink colored male pollinated a pink
colored female. 7 seeds were created and later grew into plants with
3 having pink flowers, 2 with white flowers, and 2 with red flowers.
a) Create a pedigree
for these 9 flowers
(make the offspring
any gender you
wish).
b) Create a Punnett
square for the
parents.
c) Probability of
growing pink?
50%
RW
RW
RW
RW
RW
WW
WW
RR
RR
Incomplete vs. Codominance
Codominance: Both equally expressed
Red flowers + White flowers =
Incomplete Dominance: alleles blend
Red flowers + White flowers =