Home Biol 4241 Luria-Delbruck 1943 Hershey-Chase 1952 Meselson-Stahl 1958 Garapin et al. 1978 McClintock 1953 King-Wilson 1975 Sanger et al. 1977 Rothberg et al. 2011 Jeffreys et al. 1985 Bacterial Genetics Mutational Dissection Gene Regulation Cell Number: Cancer Sex Determination Complex Pattern Formation NextGen Sequencing Bioinformatics Hamer et al. 1993

Introduction

Bacteria are ubiquitous and abundant Bacterial genetics is an important part of molecular biology 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 F-

The 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

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

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.