Obtaining variants

1. Definitions

2. Screens or selections

   1. Examples

   2. Look for phenotype results from the alteration of gene activity.

   3. Phenotypes can differ in different situations

3. Saturation mutagenesis

   1. Definition

   2. Why do this?

   3. Calculation (Poisson)

Demonstration of random mutations: The Luria/Delbrück Experiment (1943)

Characterizing putative mutants by whether they breed true.

1. Phenocopy.

2. Only some of the progeny will have the mutant phenotype.

   1. Dominantly-acting alleles in a heterozygote

   2. Penetrance and expressivity.

3. All animals have the same mutant phenotype.

Independent assortment of traits

1. With two genes one expects Mendelian ratios of 9:3:3:1

2. Some mutations can give altered ratios

Approaches to Genetics problems (in handout)