lecture 2 - principles of genetic analysis

Question 1

Why screen for mutants?

Answer 1

In a screen for mutants you do not make any assumptions about the genes you might find
You do not need to know about the underlying biochemical or physiological systems, or which molecules are involved
You can find many genes from one simple screen and they can all be characterised
Mutants can be used to find genes with related or interacting functions

Question 2

What is the purpose of mutagenesis screens and complementation tests?

Answer 2

Mutagenesis screens are used to identify the genes required for a particular function
Complementation tests are carried out to determine how many genes have been identified
This also gives an indication of how many genes are required for the biological function being investigated
Mutagenesis screens are important because they often reveal a series of alleles (or an allelic series)

Question 3

What is an allelic series?

Answer 3

An allelic series is a collection of different mutant alleles for a gene
These are different mutations in the same gene
Each allele can have different amounts of gene activity which can lead to slightly different phenotypes
Cystic fibrosis (CF) is a recessive genetic disease caused by mutations in the CFTR (Cystic Fibrosis Transmembrane Conductance Regulator) gene
Some result in partial or residual CFTR activity and the phenotype of patients varies widely because of these different alleles

Question 4

How can mutants be used to find other genes with similar or related functions?

Answer 4

Screen for new mutations in the mutant background - this is known as a modifier screen
Modifier screens can detect two types of mutations:
Those that suppress of the original mutant phenotype
- these new mutations are known as suppressors
Those that enhance the original mutant phenotype
- these new mutations are known as enhancers
Enhancers and suppressors are also know as modifiers