Lack of Dominance
Objectives:
After completing this section, you should:
1. Define lack of dominance
2. Contrast complete dominance with a lack of dominance
3. Recognize where the results from monohybrid crosses or pedigrees can be
explained by the concept that alleles controlling a trait show a lack of dominance
4. Predict the outcomes from crosses in families where the trait of interest is
controlled by alleles that have a lack of dominance
5. Apply the concepts of dominance and lack of dominance to explain how genes
control phenotypes at the molecular level.
6. Predict what happens to phenotype and genotype variation when there is a lack
of dominance and multiple alleles controlling a trait in a family.
Some key terms:
Complete dominance
Lack of dominance
Incomplete dominance
Co-dominance
Over dominance
Multiple alleles
Pleiotropy
On line lessons: none
Gene____: Controls which proteins are made and placed on the
red blood cell surface
Allele: Different versions of this gene
A allele: ______
B allele: ________
Phenotype: Type A is the genotype IA IA
Type B is the genotype IB IB
O allele: _______
IA IO
IB IO
Type AB is the genotype IA IB
Type O is IO IO
Apply the term dominant allele to the above
Apply the term lack of dominance to the above
Weed Genetics Example
Shattercane Story: Shattercane could be killed by a number of herbicides
called ALS enzyme inhibitors
After a few years, many shattercane plants in farmers’ fields could resist the
application of these ALS inhibitor herbicides.
Scientists at UNL collected the shattercane plants and did genetic studies.
ALS susceptible X ALS resistant (true breeding lines)
F1: All the F1s sprayed with the ALS inhibitor herbicide were hurt by the
herbicide but did not die.
Explanation?
Experiment you would do to test your explanation?
Expected results