1. Complex Patterns of Inheritance

2. Incomplete Dominance
One allele does not over shadow the other, they mix together
Use RR, R’R, R’R’
Ex. Carnations
A red carnation mated with a white carnation makes a pink carnation.
Ex. Snapdragons
Ex. Carnations

3. Cross a red snapdragon with a pink snapdragon:
Parental Genotypes:
Phenotypic Ratio:
Genotypic Ratio:

4. Cross a red snapdragon with a white snapdragon:
Parental Genotypes:
Phenotypic Ratio:
Genotypic Ratio:

5. Co-Dominance
Both alleles are expressed equally. One allele does not over shadow the other.
Use HRHR HRHW HWHW
Ex. Roan Cattle
Red and white hairs are present
Ex. Some flowers

6. Cross a roan cow with a roan bull
Parental Genotypes:
Phenotypic Ratio:
Genotypic Ratio:

7. Sex Linked Normal Female XAXA Carrier Female XAXa Affected Female XaXa
Traits that are carried on the X chromosome
Females need 2 recessive copies of the allele to express the trait, if they receive one they are a carrier.
Males only need one copy of the allele to express the trait, this is why sex linked traits are more prevalent in males.
Use X and Y chromosomes with the allele as a subscript to represent the trait
Normal Female
XAXA
Carrier Female
XAXa
Affected Female
XaXa
Normal Male
XAY
Affected Male
XaY

8. Cross a carrier female with a normal male
Parental Genotypes:
Phenotypic Ratio:
Genotypic Ratio:

9. Multiple Alleles & Co-dominance
In humans blood type is controlled by 3 alleles
A, B, O
A & B are co-dominant – O is recessive
Type O: OO or ii
Type A:
AA / IAIA (homozygous)
AO / IAi (heterozygous)
Type B:
BB / IBIB (homozygous)
BO / IBi (heterozygous)
Type AB
AB / IAIB

10. Blood Types Blood Type Blood Type That Can Be Received
Type of Antigens Present
Type of Antibodies Produced
A ( IA )
A and O
A antigens
B antibodies
B ( IB )
B and O
B antigens
A antibodies
O ( i )
Universal Donor
Only O
No antigens
A and B antibodies
AB ( IAIB ) Universal Recipient
All types
A and B antigens
No antibodies

11. Multiple Alleles
Traits that are controlled by one gene with several different alleles.
Ex. Coat color in Labs is controlled by 4 different alleles, 5 coat colors are possible.

12. Polygenic Traits Traits that are carried on more than one gene.
Exs: hair color, skin color, height.
A a C c
B b