1. Variations in Heredity
Learning Goal: To explore traits that show incomplete and codominance.
Success Criteria:
explain the difference between complete dominance, incomplete dominance, and codominance
explain how blood type is inherited and how blood type is used to determine compatibility for transfusions
determine phenotypes and genotypes for traits that show incomplete and codominance
Why do we resemble our parents? (We resemble our parents because we inherit traits from them.) 2. Why does asexual reproduction result in genetic clones? (During asexual reproduction, the organism makes a copy of itself without combining its genes with those from another organism. The offspring are a genetic copy of the single parent.) 3. Why are the offspring of sexual reproduction not genetically identical to either parent? (During sexual reproduction, genes from two individuals combine to produce offspring with new combinations of genes.)

2. Percentage Of Blood Types In Canada & World Map Of ABO Blood Types
What Blood Type are You?
Type A
Type B
Type AB
Type O
one of the genes that controls flower colour (C) has one allele for red (CR ) and one allele for white (CW). A homozygous CR CR plant will produce red fl owers, while a homozygous CWCW plant will produce white fl owers. However, the heterozygous plants will produce pink fl owers (CR CW).
Percentage Of Blood Types In Canada & World Map Of ABO Blood Types

3. Incomplete Dominance
in some instances, neither of the alleles controlling the trait are dominant
therefore a blending of traits occurs in heterozygotes
eg. snapdragon flowers
genes that controls flower colour (C) has one allele for red (CR ) and one allele for white (CW)
CRCR plant will produce red flowers
CWCW plant will produce white flowers
(CR CW) will produce pink flowers
Note: in the F2 generation the phenotype ratio is the same as the genotype ratio (1:2:1)
one of the genes that controls flower colour (C) has one allele for red (CR ) and one allele for white (CW). A homozygous CR CR plant will produce red fl owers, while a homozygous CWCW plant will produce white fl owers. However, the heterozygous plants will produce pink fl owers (CR CW).

4. Codominance again, both alleles for a trait may be equally dominant
rather than blending, both alleles are expressed in the heterozygous individual
eg. shorthorn cattle
a red bull (HRHR) crossed with a white cow (HWHW) will produce a roan calf (HRHW) that has intermingled white and red hair
one of the genes that controls flower colour (C) has one allele for red (CR ) and one allele for white (CW). A homozygous CR CR plant will produce red fl owers, while a homozygous CWCW plant will produce white fl owers. However, the heterozygous plants will produce pink fl owers (CR CW).

5. Codominance & Dominance: Blood Types
human blood type is both a codominant and dominant genetic trait
blood type gene has three possible alleles: IA, IB , and i which code for different antigens (i.e. A or B) or no antigens (i.e. i)
result in the four major blood types: A, B, AB, and O
type AB blood is an example of codominance and type IAi blood & type IBi blood are examples of dominant inheritance
Possible Genotypes
Phenotypes ii
Type O
IAIB
Type AB
IAIA
Type A
IAi
IBIB
Type B
IBi
one of the genes that controls flower colour (C) has one allele for red (CR ) and one allele for white (CW). A homozygous CR CR plant will produce red fl owers, while a homozygous CWCW plant will produce white fl owers. However, the heterozygous plants will produce pink fl owers (CR CW).

6. Codominance & Dominance: Blood Types
individuals who receive blood transfusions must receive blood that is compatible with their own
antibodies are proteins found in blood which recognizes and attacks particles foreign to the body (antigens)
for example, someone with type A blood forms antibodies against the type B antigen (since it is foreign to this person)
giving this person blood containing the B antigen will cause an immune response
one of the genes that controls flower colour (C) has one allele for red (CR ) and one allele for white (CW). A homozygous CR CR plant will produce red fl owers, while a homozygous CWCW plant will produce white fl owers. However, the heterozygous plants will produce pink fl owers (CR CW).

7. Codominance & Dominance: Blood Types
in an emergency situation when there is no time to test the patient’s blood type O blood may be used
type O blood is known as the “universal donor”
type AB blood is the “universal recipient”
Blood
Type
Antigens
Present
Antibodies
Can receive blood from:
Can donate blood to: A
anti-B
A and O
A and AB B
anti-A
B and O
B and AB AB
both A and B
no antibodies
A, B, AB, O
AB only O
no antigens
both anti-A and anti-B
O only
one of the genes that controls flower colour (C) has one allele for red (CR ) and one allele for white (CW). A homozygous CR CR plant will produce red fl owers, while a homozygous CWCW plant will produce white fl owers. However, the heterozygous plants will produce pink fl owers (CR CW).

8. Homework
complete worksheet “Incomplete and Codominance Practice Problems”