Thursday, 11 February 2021

Transformation of genetic recombination in bacteria

Genetic analysis of recombination in bacteria

Defination of recombination :
Bacterial recombination is characterized by DNA Transfer from one organism called donor to another organism as recipient.

Genetic recombination process in Bacteria occurs in 3 main ways -
1) Transformation,
2) Conjugation,
3) Transduction.

Bacteria (Prokaryotes) do horizontal gene transfer at the time of recombination.
Gene transfer has 2 machanism
1) Horizontal gene transfer - in this machanism gene transfer between two independent organisms. E.g. conjugation, transduction and transformation.
2) Vertical gene transfer - in this machanism gene transfers parent to offspring. E.g. sexual reproduction by Binary Fission in Prokaryotes.

The fragment of DNA that is Transferred during horizontal gene transfer from donor to recipient is referred as Exogenote.
The recipient bacterial cell's own genetic material is called Endogenote.

A bacterial cell that has received an exogenote is initially deploid for part of its genome is called merozygote(partially diploid).

Recombination generally requires that the two DNA molecules be homologous (very similar/ not identical). If they are non homologous due to origin from different species than recombination is unlikely.

Exogenote are often degraded rapidly so that there is a race between degradation of exogenote and recombination.

Transformation :

Transformation is the process of uptake a naked DNA molecule or fragment from the medium by a cell and it's incorporation into chromosome of recipient.

Introduction :

- Transformation was first gene transfer mechanism discovered in bacteria by Fred and Grifth in 1928.
- Transformation may be natural or artificial.
Natural transformation is a rare event and occur both in gram positive and gram negative bacteria.

Competence -
- The ability of recipient bacterium to take up free DNA and become transformed is called competence. It is an inheritable characteristic.
- Competent bacteria that take up DNA from environment at high frequency encode proteins called competence factor.
- Competence factor facilitate binding of DNA fragment to cell surface and uptake of DNA in cytoplasm. e.g. competent bacteria produces competent protein which binds to foreign DNA on cell surface and then uptake by cytoplasm.

Process of Transformation :

Transduction in bacteria
1). Cell free transforming DNA in the bacterium immediate environment can be naturally released when cells die and lysis.

2). Once DNA comes in contact with competent bacteria, linear dsDNA converts to single stranded DNA and one strand is degraded.
3). Single stranded DNA (exogenote) is unstable and degraded unless they are integrated into endogenote by homologous recombination.

Genetic analysis of transformation :
- Transformation is used for gene mapping.
- Genetic analysis of Transfer together is they are near enough to be carried on same DNA fragment.
- Frequency of transformation is inversely proportional to the distance between two genes.


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