Lecture 3 Flashcards
Why are bacteriophages good for genetic study of mutations?
Viruses that infect bacteria are easily and rapidly grown, they are genetically the simplest organisms and have similar genetic mechanisms to the host cells and millions can be analysed very easily (allowing for detection of very rare events).
What is a bacteriophage plaque?
Bacteriophage plaques are the “holes” in a lawn of bacteria where the bacteria have been killed by the phage.
What analysis did Benzer do which involved two different mutant types infecting a bacteria?
He did complementation analysis: The production of a wild-type phenotype when two different mutations are combined in a diploid or a heterokaryon, e.g put them in as pairs with different mutations of the rII mutants to see if they could work together to grow. If the mutations were in different rII genes complementation occured leading to cell lysis and release of progeny phage. If the mutation was in the same gene this would not occur.
What were the results from Benzer’s complementation analysis?
Some pairs of mutants could form progeny phage (complementation), some pairs did not give rise to progeny phage (no complementation). All rIIA mutants could complement all rIIB mutants and vice versa, but no rIIA mutants or rIIB mutants could complement bacteriophages with mutations in the same gene.
What is recombination and what does it lead to?
Recombination is a process that generates new gene combinations. It will lead to one chromosome with two mutations and one with none from two chromosomes with one.
What did Benzer do involving recombination?
Benzer infected E.coli strain B with pairs of mutants (all rII mutants grow on this) and then infected progeny phage onto strain K12, plaques indicated wild type phage had been formed inside the strain B cells. The numbe of plaques indicated the frequency of recombination events, corresponding to the distance between the mutations in DNA (closer, means less likely).
What were Benzer’s conclusions from his genetic map?
All of benzers mutation could be linearly arranged with spots marking the sites where mutations occur (size of which determines how many seperate mutations occur at that site, some got more than others) because this genetic map was linear the genes were likely to be linear, most mutations are changes only at one base pair (could be deletion) and some sites have loads of mutations (hotspots).
How are bacteriophages and eukaryotic viruses similar?
viruses affect a very wide range of animals and plants, eukaryotic viruses are genetically simple (10-100 genes typically), genomes can be single or double stranded DNA, or RNA, range from structurally simple to complex, rely on the host cells to provvide the nutrients and chemicals needed to make more viruses and can kill the host cell or become integrated into the genome.
