MeselsonWiegle

MeselsonWiegle - c +, and + mi ) results in a different...

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
The Meselson and Wiegle Experiment Experiments beginning in the 1940s where E. coli B strain bacteria were coinfected with two rII mutant bacteriophage resulting in progeny that could produce plaques on a lawn of E. coli K provided the first genetic evidence for recombination. The first physical evidence of recombination came from experiments by Matthew Meselson and Jean Weigel in 1961 (see slide 4 of the Recombination slide set: Griffiths fig 19-2). They used two strains of a bacteriophage called lambda ( λ ) which contains a linear DNA genome. One strain was wild type for the genetic markers c and mi and the other had mutations at both of these sites. They grew the mutant c mi phage in media containing “heavy” carbon ( 14 C) and nitrogen ( 15 N), while the + + wild type phage was cultured in media consisting of “light” isotopes of these elements. Both wild type and mutant phage of these strains produce plaques but each combination (+ +,
Background image of page 1
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: c +, and + mi ) results in a different plaque morphology. After coinfecting E. coli with both strains of λ , progeny phage were isolated from plaques and separated according to their varying densities using a cesium chloride centrifugation. When the centrifugation was completed, a smear of phage bands was observed in the centrifuge tube (a single band is normally observed when bacteriophage of the same size/density are centrifuged through a cesium chloride gradient). Intermediate bands were carefully removed by inserting a fine needle through the centrifuge tube. After several washing steps to remove all of the cesium chloride, phage from individual intermediate bands were used to infect E. coli . Some of the resulting plaques had morphology consistent with a c + genotype, indicating that a physical exchange of light and heavy DNA had occurred in the formation of the recombinant phage....
View Full Document

This note was uploaded on 05/17/2011 for the course MCDB 101A taught by Professor Thrower during the Spring '08 term at UCSB.

Ask a homework question - tutors are online