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Table of Contents
Why Do Genetics
Genetic Terms
More Terms
Basic Molelcular

More Basic Concepts
Mutation Frequency
Chemical Mutagenesis
Frameshift Mutation
DNA Repair
Mutation Summary
Detecting Mutants
Complex Mutation
Insertion Sequences
Compound Transposons
Complex Transposons
Models of

Transposition Summary
Mutagenesis in vitro
Effects of Mutations
Plasmids and

F Factor


Two Factor Crosses
Deletion Mapping
Other Mapping Methods
Strain Construction
Inverse Genetics
Gene Isolation
Characterization of

Sequence Data
General Approaches
Final Summary
Problem Set 1
Problem Set 2

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Defense of method

©2000 written by Gary Roberts, edited by Timothy Paustian, University of Wisconins-Madison


The purpose of this section of the course is to give you a feeling of why and how someone would profitably use genetics in the analysis of a biological question. The view presented will be reasonably subjective and prejudiced. The approach will not be historical although some topics will be briefly treated that really have only historical interest. A number of different items will come up at several points in the text, either because I could not see how to avoid that or because they deserve to be reemphasized.

The goal is two-fold: (1) to help you ask what the use of genetics might be on research problems that confront you and (2) to help you decide the proper interpretation of genetical research performed by others. For the purposes of this text, genetics will be defined as the generation, identification and analysis of mutants.


What sort of information do you get through this approach? The discipline of biochemistry allows the precise analysis of biological phenomena, but it is typically limited to analyses in vitro. Genetic analyses are less precise and direct, but they provide an understanding of the system in vivo. The following is not intended to be an all-inclusive list of "uses" of genetics, but provides some idea of the range of possibilities:

  1. Organization of Genes. The generation and characterization of mutants provides insight into the number of genes involved, their relative location, and their transcriptional organization.

  2. Functional Studies. Biochemical characterization of mutants that have been genetically characterized and defined as affected in a single gene provides: (a) an indication of the various roles that gene product plays in vivo; (b) correlation of a gene and its protein product confirms the identity of the actual protein performing a given function in vivo; (for example, purifying a protein capable of donating electrons to enzyme X in vitro does not prove that it is the in vivoelectron donor. The isolation of a mutant that fails to reduce enzyme X in vivo and the subsequent identification of a protein lacking or altered in that strain would provide a strong argument that the missing protein was the in vivo donor.). (c) Analysis of metabolites accumulated in mutants provides an indication of metabolic pathways and correlates the mutation (and therefore the affected gene) with a biochemical step. Similarly, analysis of which externally supplied pathway intermediates "bypass" the genetic block confirms pathway characterization and gene-function assignments.

  3. Structural Studies. The biochemical characterization of a number of altered versions of a gene product provides insight into the relationship of the structure to the function of the protein. This is particularly true for proteins whose structure has been determined by X-ray crystallography: the sequence position of the mutation within the gene allows the correlation of the resulting biochemical defect with a position on the 3-D protein structure.

  4. Biotechnology. There are obvious biotechnological values in the generation of mutants with desirable properties like overproduction of the desired gene products or metabolites, production of novel gene products or metabolites, or the easily regulated production of gene products or metabolites.

The specific power of bacterial genetics derives from the possibility of analyzing very large numbers of events (because bacteria are very small) and of performing selections (see section II), in addition to the fact that bacteria perform a vast number of important biological roles in and of themselves.

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