Advanced Genetics

Incomplete Dominance and Codominance

These traits appear to blend in offspring, for example:

RR(red) x WW(white) = RW (pink)

What happens if two pink flowers are crossed (RW x RW)?


What happens if a pink and a red flower are crossed?


Roan coloration in cows is codominant - this means both alleles are expressed
Pink coloration in flowers is incomplete dominance - neither is expressed.

What offspring ar expected from a cross between roan and white cows?



Multiple Allele Traits

Blood types are controlled by three alleles: A, B, O

O is recessive, A and B are codominant.

A person with type A blood can be genotype AA or AO
A person with type B blood can be genotype BB or BO
A person with type AB blood can only be genotype AB
A person with type O blood can only be genotype OO

What is the expected blood type of children who have parents who are AB and O?


What are ALL of the possible blood types of children whose parents are A and O?



Polygenic Traits

bell curve

Traits controlled by many genes, resulting phenotypes are in a range with a central average. Each allele intensifies or diminishes the phenotype; Examples: height, skin color, seed color in wheat

(P) AABBCC x aabbcc
(F1) AaBbCc x AaBbCc
(F2) Seven possible phenotypes

Sex Linked Traitsfruitfly

Alleles are located on the sex chromosomes (XX and XY)

Example:  In fruit flies, eye color is a sex linked trait.  Red is dominant to white.

Environment and Phenotype

Environmental factors, such as temperate can affect the expression of some genes



Epistatic Alleles

In labradors, coat color is controlled by two sets of alleles. Black is dominant to brown, but yellow is epistatic, when two yellow alleles are present (ee), the yellow coat color is expressed, independent of the brown/black alleles present.


1. A black lab (BBEe) x yellow lab (bbee)



2. A chocolate lab (bbEe) x black lab (BbEe)



3. Two black labs (BBEE x BbEe)