Mutations

Changes in the coding sequence of genes

Fine Structure Mutations -

AUG.UUU.AGG.GGG.............UGG.UGA - DNA/RNA
MET.PHE.ARG.GLY..............TRP.STOP - PROTEIN:

Mutation (U to C)
AUG.UUC.AGG.GGG.............UGG.UGA
MET.PHE.ARG.GLY............TRP.STOP

AUG.UUU.AGG.GGG.............UGG.UGA
MET.PHE.ARG.VAL............TRP.STOP


Mutation (G to A)
AUG.UUU.AAG.GGG.............UGG.UGA
MET.PHE.LYS .VAL..............TRP.STOP

DNA: AUG.UUU.AGA.GGG.............UGG.UGA
PRO: MET.PHE.ARG.GLY............TRP.STOP

Mutation (A to U)
DNA: AUG.UUU.UGA.GGG.............UGG.UGA
PRO: MET.PHE.Stop

AUG.UUU.AGG.GGG.............UGG.UGA
MET.PHE.ARG.VAL............TRP.STOP
Insertion of an A
AUG.UAU.UAG.GGG.G.............UG.GUG.A
MET.TYR.STOP....
 

AUG.UUU.AGG.GGG.............UGG.UGA
MET.PHE.ARG.VAL............TRP.STOP
Deletion of a G
AUU.UUA.GGG.GG.............U.GGU.GA
ILE.LEU.GLY.GLY.... GLY.(SER,ARG?)
 

Forward Vs Reverse Mutation

How many different mutations are possible within a single
codon such as UUU?

AUG.UUU.UCA.GGG.............UGG.UGA
MET.PHE.SER.GLY............TRP.STOP
Mutation (C to A)
AUG.UUU.UAA.GGG.............UGG.UGA
MET.PHE.Stop
With a suppressor in the system
AUG.UUU.UAA.GGG.............UGG.UGA
MET.PHE.LYS.GLY............TRP.STOP
 

In E. coli a nonsense suppressor mutation will not only suppress the expression of a bacterial gene it will also suppress a viral gene.

Let us look at mutation possibilities of a nonsense codon such as UAA or "amber"

What are the amino acid coding possibilities?

Now if we assume that there is a mutant tRNA that misreads the code what would we have?

Amber

"One evening, when Bernstein was a student at Cal Tech, he went down to Seymour Benzer's lab to try to persuade his friends, Charles Steinberg and Richard Epstein, to to to the movies with him. He was unsuccessful, because Steinberg and Epstein were busy making mutant phages and could not leave. Instead, they persuaded Bernstein to make himself useful and help them. As they worked, they explained the experiments to Bernstein, who became intrigued with the project and made a prediction about its outcome. The others disagreed, so they made a bet. Whoever guessed correctly about the characteristics of the mutant phage would get to name the mutant. Bernstein guessed that it would grow on a mutant strain of E coli, but not on wild-type He proposed to name the mutant phage for his mother, Mrs. Bernstein." (Weaver and Hedrick. 1989. Genetics. P311.) The name was later translated from German to English, from "Bernstein" to "amber" which did stick.

Conditional Lethal Mutations - The isolation of mutants that would grow under one condition but not another was one of the most powerful tools of genetics.

Mobile Elements Barbara McClintock -

Crossing over is the breakage and reunion of chromosomes - just like the sister chromatid exchange that we covered early.

Inversion of element

Excision or loss of element


Text iGenetics by Peter J. Russell


This web site is provided for instruction in Botany and Zoology 342

by Kenneth G. Wilson,
Professor of Botany
Miami University
wilsonkg@muohio.edu