Essential Question: What is the
difference between incomplete and
co-dominant traits?
-
Different forms of a genes are alleles.
-
The principal of dominance states that
some alleles are dominant and others are
recessive.
-
Heterozygous genotypes always shows
the dominant trait.
Neither allele is dominant in expressing
its trait.
- Each allele is represented by a different
letter.
- Heterozygous forms will be expressed as a
blend of the homozygous traits.
-
 In
some plants the alleles for flower color show
incomplete dominance
 RR = Red flowers
 WW = White flowers
 RW = Pink flowers
 Straight hair
and curly hair are incomplete
dominant and people who are heterozygous
have wavy hair.
 What are
the genotypes for each trait if S is the
allele for straight and C is the allele for curly?
Straight
SS
Curly
CC
Wavy
SC
Set up the punnett square for a wavy haired
woman to marry a curly haired man.
wavy haired woman:
______ SC
curly haired man:
CC
______
SC
CC
C
C
S
SC
SC
C
CC
CC
Based on the Punnet square what percentage
of the offspring have:
0%
Straight hair: ______
50 %
Curly hair: _____
50 %
Wavy hair: _____
SC
CC
C
C
S
SC
SC
C
CC
CC
SICKLE CELL ANEMIA
Homozygous Dominant (AA) –Normal
Heterozygous
(Aa) –Partial Disease
Homozygous Recessive (aa) –Disease
Being heterozygous is a benefit because it
protects them from malaria
- “co”-together (cooperate-work
together, cohabitate-live
together)
- In the heterozygous form, both
traits appear together.
Blood Types
Humans have 4 blood types:
A, B, AB, O
Only 3 alleles: A,B,O
Alleles A and B are codominant.
Allele O is recessive.
Phenotype
A
B
AB
O
Genotype
A
A
II
A
O
II
or
B
B
B
O
I I or I I
A
B
II
O
O
I I
Dad has type O and mom has type AB.
Set up the punnett square.
Dad genotype =
IOIO
______
Mom genotype =
AIB
I
______
O
O
I I
IA
IAIB
IB
O
I
IAIO
IBIO
O
I
A
O
II
B
O
II
COPY DOWN AND FILL IN THE SENTENCE BELOW:
In simple dominance the heterozygous genotype
shows the __________ trait. This is different from
incomplete and codominance because in incomplete
dominance the heterozygous trait shows a
____________ between the dominant and recessive
traits, while in codominance ______ traits are show.