This document discusses three mechanisms of gene transfer in prokaryotes: conjugation, transformation, and transduction. Conjugation involves the transfer of genetic material between bacteria via cell-to-cell contact through sex pili. Transformation refers to the uptake of naked DNA by competent bacterial cells. Transduction is the transfer of DNA from one bacterium to another via bacteriophages. The document provides historical context and methodological details for each of these gene transfer mechanisms.

1. OF GENE TRANSFER INMECHANISM
PROKARYOTES
Haider hashim alsharqi
Azad university

2. INTRODUCTION
• Gene transfer is defined simply as a technique to efficiently
and stably introduce foreign genes into the genome of target
cells.
• The directed desirable gene transfer from one organism to
another and the subsequent stable integration & expression
of
foreign gene into the genome is referred as genetic
transformation.
• Stable transformation occur when DNA is integrated into
host
genome and is inherited in subsequent generations.
• The transferred gene is known as transgene and the
organism that
develop after a successful gene transfer is known as
transgenic.

3. METHODS OF GENE TRANSFER
TRANSDUCTION&TRANSFORMATION&CONJUGATION

4. CONJUGATION
Definition
It is the process of gene transfer via sex pili between
cells of opposite mating types that are in physical contact
(cell-to-cell) with each other.
History
For the first time JOSHUA LEDERBERG & EDWARD
L.TATUM in 1946 presented the evidence for bacterial
conjugation i.e. a process of transfer of genetic material
by cell-to-cell contact.

5. METHODOLOGY
 Requires the presence of a special plasmid called the F plasmid.
 Bacteria that have a F plasmid are referred to as F+ or male. Those
that do not have an F plasmid are F- or female.
 The F plasmid consists of 25 genes that mostly code for
production of sex pilli.
 A conjugation event occurs when the male cell extends his sex pilli
and one attaches to the female.
 This attached pilus is a temporary cytoplasmic bridge through
which a replicating F plasmid is transferred from the male to the
female.
 When transfer is complete, the result is two male cells.
 When the F+ plasmid is integrated within the bacterial
chromosome, the cell is called an Hfr cell (high frequency of
recombination cell).

9. TRANSFORMATION
Definition
Transformation refers to the transfer of relatively
small segment of naked DNA from donor cell(male) to
competent recipient(female) cell.
HISTORY
Bacterial transformation was first discovered by
GRIFFITH in 1928 between the two strains of
Streptococcus (Diplococcus) pneumonia which
causes pneumonia in humans and mice.

10. GRIFFITH’S EXPERIMENT
 The RII strain (non-pathogenic, rough colony forming, mutant
strain) did not cause death to mice, whereas the SIII strain
(virulent) caused death to mice & The heat killed SIII strain
also showed similar results like that of RII strains.
 However, when heat killed SIII strain was mixed with RII strain
and injected into mice, the mice died.
 This induction in change of RII strain was called
TRANSFORMATION.
 Avery, Macleod and Mc Carty(1994) conducted the
experiment and demonstrated that heat killed SIII strain
transformed RII stain into virulent form which caused death of
mice
 The transforming ability was not altered by treatment with
enzyme or by RNase, but was completely destroyed by DNase.
 These findings showed that DNA has the ability to carry
hereditary information

13. TRANSDUCTION
DEFINITION
Transfer of DNA from one bacterium to
another via Bacteriophage
HISTORY
The phenomenon of transduction was first
discovered by ZINDER & LEDERBERG in 1952.
He discovered this while searching for sexual
conjugation in Salmonella species.

14. PHASES OF TRANSDUCTION
* Transduction happens through either the lytic cycle or
the lysogenic cycle.
* If the lysogenic cycle is adopted, the phage chromosome is
integrated (by covalent bonds) into the bacterial
chromosome, where it can remain dormant for thousands
of generations.
* If the lysogen is induced (by UV light for example), the
phage genome is excised from the bacterial chromosome
and initiates the lytic cycle, which culminates in lysis of the
cell and the release of phage particles. The lytic cycle leads
to the production of new phage particles which are
released by lysis of the host.

17. The end