1. Variations in Heredity
Section 5.2

2. 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

3. What Blood Type are You? Canadian Blood Types Type A Type B Type AB
Type O
Canadian Blood Types

4. Incomplete Dominance
in some instances, neither of the alleles controlling the trait are dominant
therefore a blending of traits occurs in heterozygotes
e.g. 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)

5. Incomplete Dominance
1. What are the phenotypic and genotypic ratios for the F1 and F2 generation of a cross between and white and red snap dragon?
2. Indicate the ratios that would be expected if the following crosses are made:
a) red x pink
b) white x white
c) pink x pink

6. Codominance again, both alleles for a trait may be equally dominant
rather than blending, both alleles are expressed in the heterozygous individual
e.g. 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

7. Codominance
3. A red bull (without wings!!!) is crossed with a white cow. What is the F1 genotype and phenotype ratios?

8. Codominance & Dominance: Blood Types
three blood type alleles: IA, IB , i
results in the four major blood types: A, B, AB, and O
alleles for blood types A and B are codominant
blood type O is homozygous recessive

9. Codominance & Dominance: Blood Types
Possible Genotypes
Phenotypes ii
Type O
IAIB
Type AB
IAIA
Type A
IAi
IBIB
Type B
IBi
1. human blood type both a codominant and dominant genetic trait

10. Codominance & Dominance: Blood Types
A human blood group or “type” is a group of red blood cells that have the same antigen protein markers on the cell surface

11. Codominance & Dominance: Blood Types
antibodies are proteins found in blood which recognize and attack 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)
individuals who receive blood transfusions must receive blood that is compatible with their own
giving this person blood containing the B antigen will cause a dangerous immune response

12. Codominance & Dominance: Blood Types
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
1. in an emergency situation when there is no time to test the patient’s blood, type O blood may be used
2. 42% A, 9% B, 3% AB, 46% O

13. 4. A woman with homozygous type A blood has a child with a man who is heterozygous B. What are the genotypes and phenotypes possibilities of the offspring?

14. 5. A woman with A type blood marries a man with B type blood
5. A woman with A type blood marries a man with B type blood. They have a child with type O blood.
The man says the child cannot be his. Is he correct? Show your work to prove you are right.
If this child belongs to this father, what were the chances of having this child with type O blood.

15. 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

16. Blood Lab
Inheritance Investigation

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