FAQ in bacterial genetics

What is the nature of bacterial chromosome?

Bacterial chromosomes are circular and supercoiled. Borrelia burgdorferi and Streptomyces have linear chromosomes. Bacteria have single set of chromosomes, ie. they are haploid.

What is mutation?

Sudden heritable change in a nucleotide sequence. They are classified as base substitution, frame shift mutation and insertional inactivation.

What is mutatiion rate?

Mutation rate is the estimation of the rate (per generation) of mutation per nucleotide, per locus, or the whole genome. With respect to antibiotic resistance, it is frequently defined as the frequency at which detectable mutants arise in a bacterial population in the presence of a given antibiotic concentration in vitro. Generally, the mutation rate in bacteria is approximately 0.003 mutations per genome per cell generation.

What is base substitution mutation?

When one base is inserted in place of another, it is base substitution, when this results in a codon that causes a wrong amino acid to be inserted, it is missense mutation and when a base substitution results in the generation of a termination codon, it is nonsense mutation.

What are the methods of gene transfer between bacteria?

Transformation, conjugation and transduction.

What are the transposons or “jumping genes”?

These are pieces of DNA that move from one site to the another, either within or between the DNA of bacteria, plasmids and bacteriophage.

What is the significance of Transposons?

What are insertion-sequences?

Insertion sequences are short stretches of DNA that can move from one part of chromosome to another. They differ from transposons in that they code only for genes responsible for self-transfer. These may bring about insertional mutations by inactivating a gene or block the expression of gene by inserting insterting into promoter regions of operons.

What are integrons?

Integrons are mobile genetic elements that are able to capture and incorporate gene cassettes by site-specific recombination. The gene cassettes may contain genes for antibiotic resistance.

What are gene cassettes?

Gene cassette are a type of mobile genetic elements, which contain a gene and a recombination site. The cassettes may exist inside an integron or freely as circular DNA. Often, the gene cassettes carry antibiotic resistance genes.

What is transduction?

It is the transfer of DNA from one bacterium to the another by a bacteriophage.

What is conjugation?

It is the process of genetic transfer where a bacterium with F plasmid (F+) mates with another bacterium (F-) and sends a strand of F plasmid DNA into the recipient cell through sex pili.

What is F factor?

The transfer factor, also called fertility factor is a plasmid that codes for the synthesis of sex pili and self transfer.

What is R factor?

It is a plasmid that codes for drug resistance. Its transfer to other bacteria is independent of F factor.

What is an episome?

It is a plasmid, which is known to integrate itself with the bacterial chromosome.

What is the significance of plasmids?

They code for the following properties:

What is sexduction?

The F factor is usually an episome that integrates itself into the bacterial chromosome. When such episome is transferred to F- cells during conjugation, some of the host chromosomal genes are also transferred.