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Biol 4241 Luria-Delbruck 1943 Hershey-Chase 1952 Meselson-Stahl 1958 Garapin et al. 1978 McClintock 1953 King-Wilson 1975
Rothberg et al. 2011
Jeffreys et al. 1985 Bacterial Genetics
Mutational Dissection Gene Regulation
Cell Number: Cancer
Complex Pattern Formation
NextGen Sequencing Bioinformatics
Introduction
Bacteria are ubiquitous and abundant
Bacterial genetics is an important part of molecular biology
Bacteria are easier to work with: no introns, small genome size, robust
Lederberg and Tatum discovered bacterial recombination in 1946
There are several ways bacteria can exchange DNA
Phenotypes
The study of bacterial genetics has important implications in the control of pathogenic and spoilage species of bacteria
In order to study bacteria in a laboratory environment, it's necessary to find appropriate growth conditions
Different colony properties can be studied
1) Ability to synthesize essential biochemical compounds
2) Utilization of energy sources
3) Resistance
All of these phenotypes are identified as either "growth" or "no growth"
Detecting Recombination in Bacteria
Recombination in bacteria is the result of partial and unidirectional gene transfer (in contrast to eukaryotes)
Only a part of the genome is donated by the donor and is recieved by the recipient
The fragment donated is called the exogenote, and the genome that recieves the fragment is called the endogenote.
If a cell contains both and exogenote and a endogenote, it is a "partial diploid" or a merozygote
Selective Systems
Techniques used to isolate rare mutants in a population consisting mainly of wild-type cells
Can select for antibiotic resistant mutants or auxotrophs
Bacterial Conjugation
The cytoplasm of two bacteria join by a cytoplasmic bridge
In E. coli fertility factor or sex factor (F) required for conjugation
Rare high frequency of recombination (Hfr) strains
Integrated F factor can excise itself, sometimes carrying host genes = F' plasmid
Recombination Between Donar and Recipent DNA
All cross can be defined as Hfr x FThe replication and entry starts at O(origin)
DNA is transfered to as single strained
Linear gene segments do not survive.
Exconjugate referes to the F- cell with the exogenote and endogenote
Mapping by Interrupted Conjugation
A low resolution map can be produced seeing which genes get transfered first.
To disrupt a conjugation, you can use a blender .
Can give a map of genes
Sanger et al. 1977
Sex Determination
Hamer et al. 1993
High Resolution Mapping by Recombination Frequency
Interrupted conjugation is not accurate for genes that are close together
Recombinant frequencies between two or more genes can create a high resolution map over small distances
Bacteriophage Genetics
Infection of Bacteria by Phages
Bacteriophage are viruses than infect bacteria
Contain a nucleic acid chromosome dsDNA, dsRNA, ssDNA, ssRNA
Nucleic acid surrounded by a protein coat called a capsid
Bacteriophage structure designed to inject nucleic acid into bacteria
Progeny phage assembled using host cellular machinery and lyse the cell
Free progeny phage infect neighbouring bacteria, producing a plaque within 15 hours
Plaques have characteristic morphologies that show phenotypes
Phage Cross
Recombination between two genetically different phage that infect the same cell
A phage T2 cross can be illustrated by observing two parental genotypes
Progeny phage phenotypes can be predicted based on genotypes
Analysis of phage crosses is subject to complications
F Factors Carrying Bacterial Genes
Integrated F factor of Hfr strain can exit the bacterial chromosome
Excision with IS element at non-entry site location can lead to the integration of bacterial chromosomal DNA into the plasmid.
Example: A lac gene can be incorporated into the donor plasmid
Bacterial Transformation
Transformation can alter the genotype of cells by the addition of exogenous DNA
This also has implications for mapping
Physical Interaction of Phage and Bacterial Genomes
During infection phage and bacterial DNA interact
Lysogeny
Virulent phages are always lytic
Temperate phages can be lytic or lysogenic
Integration into the genome occurs by alignment of sequences on the bacterial and phage genomes, followed by a crossover event
Triggered by phage-encoded genes which promote recombination
Transduction
The "accidental" transfer of bacterial genes through phage particles.
Can be defined as generalized or specialized
Determining Linkage from Transduction
Cotransduction is when genes are close enough that phage can transduce them as a single piece of DNA
Cotransduction happens more frequently when genes are close.
This can be used to derive linkage information about bacterial genes.