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Genetic Recombination


Exchange of genes between two DNA
molecules
Forms new combination of genes on a
chromosome

Along with mutations, contributes to genetic diversity
Types of Genetic Transfer

Vertical gene
transfer

Horizontal gene
transfer
•Occurs
during
reproduction, between
generations of cells
•Transfer
of genes
between cells of the
same generation
Mechanisms of Horizontal Transfer

Genes are naturally transferred between
bacteria using three mechanisms



•
Transformation
Transduction
Conjugation
All result in recombination

Transformation


Transfer of naked DNA from one bacterium to another
 Works best when donor and receipt are closely
related
Discovered by Fredrick Griffith in 1928 while working
with Streptococcus pneumoniae
Griffith Experiment

Avery, MacLeod and
McCarty

Showed DNA was
transforming agent

Competent cells pick up
DNA and integrate it into
chromosome

Transduction


Bacterial DNA transferred from donor to recipient via
bacteriophage
Two types of transduction
 Generalized
 Specialized
Transduction

Conjugation



Requires direct contact between cells
Only form of gene exchange in which donor survives
Mediated by plasmids
 Can code for traits that give bacteria advantage
Plasmid Types

Fertility factor

Dissimilation plasmids

Resistance factor

Bacteriocin factor

Virulence plasmids
Conjugation