1. What is Codominance?

2. What is codominance?
Codominance: condition in which both alleles of a gene are expressed in heterozygous offspring.
Example:
In certain chickens black feathers are codominant with
white feathers.
Heterozygous chickens have black and white speckled feathers.

3. Example 1:
In cows black coat color and white coat color are codominant. Heterozygous offspring will be spotted.
Black cow and White cow BB x WW
B B W BW
Genotypic Ratio:
100% BW
Phenotypic Ratio:
100% Spotted cow

4. Multiple Alleles
3 or more alleles of the same gene that code for a single trait
In humans, blood type is determined by 3 alleles –
A, B, and O
BUT each human can only inherit 2 alleles
Dominant – A and B
(codominance)
2. Recessive – O

5. How do the multiple alleles work with codominance?
Blood Type (phenotype)
Genotype A
AA or AO B
BB or BO AB O OO

6. Determine the possible blood types of the offspring when:
Mother is type AB, Father is Type A (heterozygous)
Genotypic Ratio:
25 % AA
25% AO
25% AB
25% BO
Phenotypic Ratio:
50% Type A Blood
25% Type AB Blood
25% Type B Blood
A B AA AB AO BO A O

7. Incomplete dominance
Incomplete dominance - when one allele is not completely dominant over another.
Heterozygous genotype = BLEND
Since one allele is not completely dominant over the other allele, we use two different capital letters to represent the alleles
Homozygous RR
(Red)
Heterozygous RW
(Pink)
Homozygous WW
(White)

8. Codominance Codominance - both alleles contribute to the phenotype.
Heterozygous genotype = both traits appear
Since one allele is not completely dominant over the other allele, and both traits appear together, we use two different capital letters to represent the alleles
Homozygous WW
(White)
Homozygous BB
(Black)
Heterozygous BW
(Black and White)

9. Practice Identifying A cat can be black, tan, or tabby (black & tan)
1. Incomplete Dominance or Codominance?
2. Genotypes:
black- BB
tan – TT
tabby – BT

10. Practice Identifying A sneech can be tall, short, or medium
1. Incomplete Dominance or Codominance?
2. Genotypes:
tall- TT
short – SS
medium – TS