Mutagenesis and Genetic Screens

inducing mutations with mutagens, screening mutant phenotypes, and mapping mutant phenotypes to mutant genotype

List some mutagens that induce mutations

• chemical mutagens (EMS, TMP,ENU,Formaldehyde…)

• Radiation (x-ray and radioactivity)

• transposable elements (insertions)

What is ethyl methanesulfonate (EMS)? What are the advantages and disadvantages?

A chemical mutagen that increases the rate of mutation by about 100-1000x higher than normal).

Pros and Cons:

• mutations are random (you cannot target a sequence for mutation, therefore, a homozygous mutation is nearly impossible)

• phenotypic mutations are rare (exons make up less than 5% of the genome, and most mutations do not effect genes)

• mutations can be replicated

Define haplosufficient genes

When one copy is sufficient to produce a normal phenotype, that is because the allele remaining can produce enough gene product (like protein) to maintain normal function in the organism

What can be said about the majority of mutations?

Most mutations are haplosufficient and recessive.

Define mutagenesis screening

A technique used to identify and study phenotypes by inducing mutations and observing their effects.

mutagenesis screening requirement

animals → complex multicellular organisms with specialized tissues, therefore germline mutations must occur so mutation is heritable

How do you look at the homozygous recessive phenotype of a mutation in plants?

M0 (EMS treatment, mutation created, heterzygotes crossed with wt) → M1 (two heterzygotes created) → M2 (homozygote created by selfing)

mutagenesis screening in hermaphrodites

Hermaphrodite organisms allow F1s to be self-crossed to generate homozygous mutants

Once phenotypes have been screened a particular gene can be located and studied (linkage), how?

Look at the resulting phenotypic ratios:

unlinked → 9:3:3:1

fully linked (0 m.u.) → 2:1:1:0