Mutations and Genetic analysis

gene

lowercase and italics (dnaA)

RNA

• mRNA is the same as a gene

• sRNAs have protein nomenclature

protein

no italics and uppercase first letter

+

has the phenotype

-

does not have the phenotype

auxotrophic mutants

mutants that are deficient at making or using something

anabolic auxotroph

• synthesis defective, can’t make a particular metabolite

• must be given a metabolite to grow

catabolic auxotroph

• cells can’t use a substrate

• often sugars

• cells can’t grow if it is the only nutrient source

mutagen

something that cause mutations

selection

mutants that we want to grow

conditional lethals

null mutation in only some conditions

temperature sensitive

gene/protein is inactive at higher temperatures

cold sensitive

gene is inactive at lower temperatures

inducible conditional lethal

place the essential gene under control of an inducible promoter

mutation rate for a given phenotype

mr= m2-m1/N2-N1

phenotypic lag

delay in mutation exerting its phenotype

Darwinian mechanism

selection of random mutants

lonarckian mechanism

directed evolution

Transitions

purine→purine or pyrimidine→pyrimidine

transversions

purine→pyridine (disruptive)

synonomous

base change in ORF that does not change amino acid sequence of protein (wobble position)

non-synonomous

base change in ORF that does change the amino acid sequence

missense

change one amino acid to another

silent

no known phenotype

null

non functional

leaky

partial function

gain of function

get a new function

nonsense

new stop codon frames

frameshift

change in reading frame +1 or -1

deletions

removal of DNA, can occur naturally

inversion

homologous recombination between inverted repeats

suppression

2nd site mutation that restores original phenotype

reversion

mutation is restored to WT sequence

TN-seq

combines TN mutagenesis with deep sequencing

Screen

all mutants grow, but mutants of interest can be identified

selection

only the mutants grow