Enhancement and suppression - AndersenLab/Genetic-Analysis GitHub Wiki

Lecture 5

Incomplete Penetrance vs. Expressivity

mutant

Not all individuals with a given genotype will express the phenotype for that genotype, nor will the phenotype necessarily be expressed to the same degree. These two phenomenon are referred to as incomplete penetrance and variable expressivity.

In a trait that is incompletely penetrant, not every individual with a given genotype will express the phenotype. For example, individuals might inherit an allele that confers the dominant phenotype but not express the dominant phenotype.

Similarly, the severity of a phenotype or disease can differ among people with the same genotype. For example, individuals with cystic fibrosis commonly inherit two copies of the ΔF508 mutation. However, the severity of the disease can vary considerably, and the disease is modulated by many additional environmental and genetic factors.

Determining Incomplete Penetrance

How is it possible to determine when incomplete penetrance is occurring? In clonal populations of organisms (such a C. elegans), it is straightforward. If the trait being examined is observed to be incompletely penetrant, then individual animals can be isolated and allowed to self-fertilize and produce offspring. You can then examine the resulting phenotypes and observe whether the trait is again observed with a similar frequency. For non-clonal populations, you must establish a pure-breeding strain.

Suppressors and Enhancers

Suppressors - make the mutant phenotype less mutant. The normal function of the suppressor gene is to act oppositely to the original mutant allele.

Enhancers - make mutant phenotypes more mutant. The normal function of the enhancer gene is to act with the same effect as the original gene.

Further Resources