Chapter 8- Bacterial and Viral Genetics: Mechanisms of Genetic Exchange

What are three characteristics that make bacteria and viruses useful for genetic studies?

Bacteria and viruses are useful for genetic studies because of their small size, rapid reproduction rates, and simple structure, which facilitate genetic analysis

Distinguish between a prototroph and an auxotroph in bacteria:

A prototroph is a wild-type bacterium that can synthesize all necessary nutrients from basic media, while an auxotroph is a mutant that requires specific nutrients to be added to the media for growth

Briefly explain the process of bacterial transformation:

Bacterial transformation involves the uptake of free DNA from the environment by a recipient cell, followed by the incorporation of the donor DNA into the recipient’s chromosome through recombination. This process alters the genetic makeup of the bacteria, potentially conferring new traits or abilities

What is the role of competence in bacterial transformation?

Competence refers to the ability of a bacterial cell to take up exogenous DNA from its environment, facilitated by specific proteins that bind and transport the DNA across the cell membrane

Auxotroph

A mutant organism that requires specific nutrients not needed by the wild-type organism

Bacteriophage

A virus that infects bacteria, often used as a tool in genetic studies

Co-transduction

The simultaneous transduction of two or more genes located closely together on the bacterial chromosome

Competence

The ability of a bacterial cell to take up exogenous (foreign) DNA from its environment

Conjugation

A process of genetic transfer in bacteria that requires direct cell-to-cell contact and a conjugative plasmid

Episome

A genetic element that can replicate independently in the cytoplasm or integrate into the chromosome

F factor

A fertility plasmid in E. Coli that enables conjugation

F+ cell

A bacterial cell that contains the F plasmid and can act as a donor during conjugation

F- cell

A bacterial cell that lacks the F plasmid and acts as a recipients during conjugation

F” plasmid

A plasmid containing the F factor along with a portion of the bacterial chromosome

Generalized transduction

Transduction in which any part of the bacterial genome can be transferred

Hfr cell (high-frequency recombination)

A bacterial cell in which the F plasmid has integrated into the chromosome, allowing for the transfer of chromosomal DNA during conjugation.

Insertion sequence (IS):

A short DNA sequence capable of transposition, often involved in the integration of plasmids into the bacterial chromosome. Then can move within or between genomes using specialized recombination systems

Parasexual processes

Processes that mimic sexual reproduction but are unique to microorganisms

Plaque

A clear area on a bacterial lawn caused by the lysis of bacterial cells by bacteriophages

Prototroph

A wild-type organism that can synthesize all necessary nutrients from basic media

Recombination frequency

The proportion of recombinant offspring resulting from a cross. This frequency depends on the distance between linked genes and is used to construct genetic maps

Specialized transduction

Transduction in which only specific genes near the phage integration site are transferred

Transduction

The transfer of DNA from one bacterium to another by a bacteriophage

Transformation

The process by which bacteria take up free DNA from the environment and incorporate it into their genome

Describe the function of the F factor in E. Coli conjugation

The F factor is a fertility plasmid in E.coli that contains genes necessary for conjugation, enabling a donor (F+) cell to form a sex pilus and transfer a copy of the plasmid to a recipient (F-) cell

Explain how an Hfr cell is generated and its significance in conjugation

An Hfr cell is generated when the F plasmid integrates into the bacterial chromosome; during conjugation, the Hfr cell can transfer a portion of its chromosome to a recipient cell, potentially leading to recombination

Outline the steps involved in chromosome mapping using conjugation

Chromosome mapping using conjugation involves interrupting mating at different time intervals, allowing for the transfer of varying lengths of the donor chromosome. By analyzing which genes are transferred at specific times, the relative positions of genes on the chromosome can be determined

What is transduction, and what role does a bacteriophage play?

Transduction is a process in which a bacteriophage transfers DNA from a donor bacterium to a recipient bacterium, leading to genetic recombination in the recipient cell

Differentiate between generalized and specialized transduction

Generalized transduction involves the transfer of any random fragment of the bacterial chromosome by a phage, whereas specialized transduction involves the transfer of specific genes located near the phage’s integration site on the bacterial chromosome

How can co-transduction frequency be used to measure gene linkage?

Co-transduction frequency measures how often two genes are transferred together by a phage. Higher co-transduction frequency indicates that the genes are located close to each other on the bacterial chromosome, providing a measure of gene linkage