INTRO TO MUTATIONS: GENE MUTATION

1/29/93, rvsd 1/26/94, 1/27/95, 1/28/98, 26 Jan 00, 31 Jan 03, 28 Jan 04, 26Jan05, 1Feb08

[SGML P 151-]GMSLG: p. 178-201, GMSLG 7^th: 464-487, GWLC, 9^th: 515-530

Variants are a manifestation of mutations.

             Two general classes:      gene mutation (point mutations, deletions) or

                                                    chromosome mutation (gross alteration in structure or number)

Can be used to               1) understand mechanisms of mutagenesis

                                       2) genetic dissection of biological function

forward mutation: alteration from wild type to variant (if nutritional: prototroph to auxotroph)

Mutant is individual carrying mutation, caused by mutagen, process mutagenesis or mutational event

change back to the standard allele is:       reverse mutation, individual = revertant

                                                                 or         reversion

                                                                 or         back mutation

Somatic mutations lead to cell clones, the mechanism for cancer.

Germinal mutation in germ line lead to mutant progeny

Location of mutation in gene affects the effect: in active site, edge of active site, away from active site

mutation effect on phenotype:             1) morphological (often affect development)       

2) conditional (temperature sensitivity)

                                                                 3) lethal (as in Manx cat)

Conditional:     example                                                                restrictive        permissive

                          siamese cat, temp sens pigment synthesis             warm                 cool

                          sickle cell carriers                                                 hypoxic             adequate oxygenation

Biochemical mutations: go from prototrophic (wild type) to auxotrophic

Resistant mutation confers resistance to some poison or inhibitor, usually by altering a preexisting protein → new function

DETECTION SYSTEMS FOR MUTAGENESIS: (p. 473)

Tradescantia: stamen color of anther hair cells in blue with P. pp is pink. line 02 is Pp, mutation in hair cell P gene shows up as pink cell. Can scan millions of cells easily. (P 474)

X-linked recessives show up immediately in males, screening males easiest, most sensitive test

Mutation rate:                   mutations/time                       usually per generation or 1/x generations

Mutation frequency:        mutations/population            population size X. (I.e., 1-500/ million)

Selective systems: (p. 477)

Microbial:      Fungi:                                Filtration enrichment to select auxotrophs (p 231)

                      Penicillin enrichment:       replicate plating on minimal vs enriched medium (p 519)

             [omit] Mutation is a random process, not induced by selective agent: (p. 195)

                      If mutation is a random event, large fluctuation in number in multiple cultures

                      If mutation is physiologically induced, then similiar number in each tube

Luria and Delbruck: fluctuation test: 20 tubes 0.2 mL medium. one with 10 ml, each inoculated with E coli, then plated on T1 seeded plates, count resistant.

Discovery of mutagenesis in 1947 by Auerbach and Robson, working for British military with mustard gas

See table 15-6 and 15-7 for list of mutagens (p. 485)