GENETIC RECOMBINATION

GENETIC

RECOMBINATION

 Genetic recombination is defined as the replacement of genetic materials between genetic elements from two different sources.

 Homologous (General) Recombination:

 It is the change between homologous DNA

sequences that are identical or very similar to each other. This phenomenon is called

crossover in classical genetics.

Gene transfer in prokaryotes

Transformation, Transduction,

Conjugation

Transformation

DNA binding protein, Cell wall autolysis, Competitive protein

RecA protein Various nuclease Competent, enough DNA size (15 genes)

 Transformation in laboratory conditions

 E. coli strains are treated with calcium ions and kept in the cold

 Disruption of cell wall structures (protoplasts)

 Transformation is also performed by electroporation, in which the holes in the membranes of the cells

exposed to electric current can pass through the DNA.

Transfection

 It is a genetic transmission system characterized by the transfer of virus DNA to cells by transformation.

 Eukaryotic cells also receive DNA similar to transformation in bacteria. The removal of

extracellular DNA molecules by phagocytosis in

eukaryotic cells without cell wall is also referred to as transfection.

 Cell-walled eukaryotic microorganisms, such as

yeasts, have a low frequency of transfection. Yeasts are artificially rendered sufficiently by various

applications to increase transfection capabilities

Transduction

General (Non-specific = Generalized = Unrestricted) transduction

Specific (Restricted) transduction:

Phage cycle

 When a temperate phage binds to the host genome, some phenotypic changes occur in the host (lysogen). This event is called the phage cycle.

 A cell infected with a tempered phage

becomes resistant to a second temperent phage infection. In this way, the ability of the bacteria to adsorb phage changes.

 Corynebacterium diphtheriae, which

causes diphtheria disease, undergoes a phenotypic change by producing toxins when infected with beta (β) phage.

In conjugation, only the conjugative plasmid is not transferred to the host cell.

Other plasmids present in donor cells, tempered phages (sexduction) or part of the chromosomal DNA of the donor bacterium may also be

transferred.

Conjugation

F plasmid

ds DNA Annular,

Elimination (curing)

Genes that provide their own replication (rep, inc, oriS) Rotating circle replication

Number of copies,

Mismatch (inc) gene region Episomal IS2, IS3, Tn1000

tra region transfer from one cell to another

 Cannot replicate when linked to chromosome

 Only the tra region is active, producing conjugation by producing pilus.

 As in transformation and transduction, there is homologous recombination

between the Hfr and F-genes in which RecA proteins are involved.

 Transposition is considered a particular type of recombination.

 Unlike homologous recombination in the cell, it does not occur between homologous base pairs.

 Only a small segment of homologous DNA is required for both DNAs to recognize each

other.

 Furthermore, RecA protein is not involved in this type of recombination. Instead, the

transposase enzyme is responsible.

 Since specific base sequences are required for this type of recombination, is called the region specific recombination.

When moving elements are linked into a gene, they disrupt the function of

that gene and cause mutation. In this phenomenon, also called transposon mutation, the movement of the

transposon is monitored by antibiotic resistance genes.