1. Incomplete Dominance & Codominance

2. Just a Recap…

3. Mendel’s Results
Mendel’s experiments illustrate complete dominance - offspring always resembled one of the two parents
The dominant allele had the same phenotypic effect whether present in one or two copies
All Mendel’s plants displayed dominant or recessive alleles. In other words, only one trait showed up.
There are some crosses where both alleles of a pair are expressed in a heterozygote

4. Crossing red and white snap dragons produces pink snap dragons
Incomplete Dominance
Incomplete dominance - heterozygous individuals have an intermediate or blended phenotype
Neither of the alleles is dominant because they do not mask the other colour
Example:
Snap dragon colour
Red flower (CRCR) and white flower (CWCW) form a pink flower (CRCW)
Crossing red and white snap dragons produces pink snap dragons

5. Questions To Consider
What are the phenotypic and genotypic ratios for the F2 generation of the snap dragon example?
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
Codominance – both alleles are expressed fully to produce offspring with a third mixed phenotype
Example: Rooster Colour
Black rooster (FBFB) and white rooster (FWFW) form a black and white rooster (FBFW)
Crossing black and white roosters produces roosters with both black & white feathers

7. Multiple Alleles Multiple alleles – more than 2 alleles for the trait
a combination of codominant and dominant genetic traits
Example: Blood Types
Blood phenotypes are controlled by a combination of two of three different alleles
Three blood type alleles: IA, IB , I
The alleles for blood types A and B are Codominant
Blood type O is homozygous recessive
BLOOD GROUPS
PHENOTYPE
GENOTYPE

8. Blood Groups & Blood Types
Erythrocytes (red blood cell) have cell-surface proteins called antigens
Blood types are based upon the types of antigens one has
Defensive chemicals called antibodies are produced by your body to protect itself from foreign cells or organisms
Antibodies circulate through the body in the fluid blood plasma
Type A
Type B
Type AB
Type O

10. Blood Coagulation
Blood clumping results when certain antibodies bind to specific antigens

11. Questions to Consider
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.