Download 11.3 Codominance and Incomplete Dominance File

Ch.11-3
Non-Mendelian Inheritance I
POINT > Describe other patterns of inheritance
POINT > Define different allele representation
POINT > Describe incomplete dominance
POINT > Describe codominance
POINT > Define polygenic inheritance
POINT > Describe examples of environmental
influence
POINT > Describe other patterns of inheritance
The mono- and dihybrid crosses we’ve studied represent
“simple” inheritance: dominant and recessive alleles and
only 1 gene per trait
Most traits do not show simple inheritance
Most alleles are not completely dominant/recessive
Usually more than just two alleles for a given gene
(an individual has two, but the population has others)
Most traits are controlled by more than one gene
POINT > Define different allele representation
We can represent alleles slightly differently: the trait
is expressed as a single capital letter
(ex. Color would be ‘C’)
Specific alleles are represented by superscript letters
Ex. Red color would be: CR
White color would be: CW
WB CHECK:
Which statement is true?
a) Most genes have two alleles
b) Most traits are controlled by one gene
c) One organism has two alleles for each gene
d) Most alleles are either dominant or recessive
WB CHECK:
The 9:3:3:1 phenotype ratio shows up
a) in the F1 of a monohybrid cross
b) in the F1 of a dihybrid cross
c) in the F2 of a monohybrid cross
d) in the F2 of a dihybrid cross
POINT > Describe incomplete dominance
Incomplete dominance: The heterozygous
phenotype is a blend between the two
homozygous phenotypes
Neither allele is fully dominant nor recessive
POINT > Describe incomplete
dominance
Ex. Snapdragon Flowers
POINT > Describe incomplete dominance
CR
P cross
CR
Genotype
100% CR CW
CW
4 CR C W : 0
CR CW
CR CW
Phenotype
100% Pink
CW
CR
CW
CR
CW
4 Pink : 0
POINT > Describe incomplete dominance
CR
F1 cross
CW
CR
CR CR
CR CW
Genotype
25% CR CR
50% CR CW
25% CW CW
1:2:1
CW
CR CW
CW CW
POINT > Describe incomplete dominance
CR
F1 cross
CW
CR
CR CR
CR CW
Phenotype
25% Red
50% Pink
25% White
1:2:1
CW
CR CW
CW CW
POINT > Describe codominance
Codominance: Both alleles are fully &
separately expressed
Neither allele is dominant over the other
POINT > Describe codominance
Ex. Shorthorn Cattle:
Differences in hair color
Red Hair
(homozygous CRCR)
POINT > Describe codominance
Ex. Shorthorn Cattle
Differences in hair color
White Hair
(homozygous CWCW)
POINT > Describe codominance
Ex. Shorthorn Cattle
Differences in hair color
Roan Hair
(heterozygous CRCW)
POINT > Describe codominance
CR
P cross
CR
Genotype
100% CR CW
CW
4 CR C W : 0
CR CW
CR CW
Phenotype
100% Roan
CW
CR
CW
CR
CW
4 Roan: 0
POINT > Describe codominance
CR
F1 cross
CW
CR
CR CR
CR CW
Genotype
25% CR CR
50% CR CW
25% CW CW
1:2:1
CW
CR CW
CW CW
POINT > Describe codominance
CR
F1 cross
CW
CR
CR CR
CR CW
Phenotype
25% Red
50% Roan
25% White
1:2:1
CW
CR CW
CW CW
WB CHECK:
A tall corn plant is crossed with a short corn plant.
The height of the offspring is intermediate between
the parents height. This is an example of
a) simple Mendelian inheritance
b) codominance
c) incomplete dominance
d) mutation
WB CHECK:
A ferret with black fur is crossed with a ferret with
brown fur. The offspring have fur that has patches
of black and brown fur. This is an example of
a) simple Mendelian inheritance
b) codominance
c) incomplete dominance
d) mutation
POINT > Describe codominance in blood types
Ex. ABO Blood Groups
Different alleles represent different antigens
on the surface of red blood cells
There are three alleles: IA IB i
POINT > Describe codominance in blood types
ABO Blood Groups:
Blood Type A
A-type antigens
POINT > Describe codominance in blood types
ABO Blood Groups:
Blood Type B
B-type antigens
POINT > Describe codominance in blood types
ABO Blood Groups:
Blood Type AB
A & B antigens
POINT > Describe codominance in blood types
ABO Blood Groups:
Blood Type O
Recessive Allele
- Neither
antigen present
POINT > Describe codominance in blood types
We use the letter “I” for blood genotypes
Genotype


Blood Type A

Blood Type B 

Blood Type AB 

Blood Type O

Phenotype
IAIA or IAi
A
IBIB or IBi
B
IA IB
AB
ii
O
WB CHECK:
One parent is a blood type A heterozygote, and the
other parent is a blood type B heterozygote. Draw
a Punnett square to show the potential offspring.
What percent of offspring will have type O blood?
POINT > Describe codominance in blood types
IA
i
IB
IA IB
IB i
i
IA i
ii
Genotypes
25%
25%
25%
25%
IA i
IB i
I A IB
ii
1:1:1:1
POINT > Describe codominance in blood types
IA
i
IB
IA IB
IB i
Phenotypes
25% A
25% B
25% AB
25% O
i
IA i
ii
1:1:1:1
POINT > Define polygenic inheritance
Polygenic traits are controlled by two
or more genes
Ex. Skin Color: at least 5-6 genes
Ex. Eye Color: 6-15 genes involved
A majority of traits fall under this category
POINT > Describe examples of environmental
influence
Environmental conditions can affect gene
expression (phenotype) by influencing
genetically determined traits
Doesn’t change genotype, just the expression
POINT > Describe examples of environmental
influence
Ex. Hydrangea
Flower color changes
depending on pH
(aluminum + more acidic
= bluer flowers)
POINT > Describe examples of environmental
influence
Ex. Arctic
Hare
Coat color changes
based on season
(amount of light, snow,
temp)
Read pages 319-321
Assess page 321 #1-2
Punnett Square WS