This document provides information about horizontal gene transfer through various mechanisms like transformation, transduction, and conjugation. It discusses that horizontal gene transfer is the transmission of genes between organisms independently of vertical descent or reproduction. The key mechanisms of horizontal gene transfer in bacteria are transformation (uptake of naked DNA from environment), transduction (transfer via bacteriophages), and conjugation (direct cell-to-cell contact via plasmids or pili). Horizontal gene transfer plays an important role in the evolution and adaptation of bacteria by allowing them to acquire new traits from other species.

1. GENOMICS PRESENTATION
ON
HORIZONTAL GENE
TRANSFER
SUBMITTED TO-
MRS. SWATI MAM
SUBMITTED BY-
SOURABH
GF/2020/3377
BTECH.BIOTECHNOLOGY SRP
5TH SEMESTER (3RD YEAR)

2. A gene determines a particular trait by encoding
for a specific polypeptide in a given organism.
Because the genetic code is (almost) universal,
an organism can potentially express a new trait
if the appropriate gene is introduced into its
genome. A gene determines the phenotype of
organism. A gene is the functional unit of
heredity. Each chromosome carry a linear array
of multiple genes. Each gene represents segment
of DNA responsible for synthesis of RNA or
protein product. A gene is considered to be unit
of genetic information that controls specific
aspect of phenotype.
GENE

3. GENE TRANSFER (GT):-
The introduction of new DNA into an existing organism’s cell, usually by vectors such as
plasmids and modified viruses. The transfer of genes between species is called GENE
TRANSFER. The new organism created is called a transgenic. The insertion of unrelated
therapeutic genetic information in the form of DNA into target cells.
The directed desirable gene transfer from one Organism to another and the subsequent
stable integration and expression of foreign gene into the genome is referred to as genetic
transformation. Transient transformation occur when DNA is not integrated into host
genome.
Two Types of gene transfer:-
1. HORIZONTAL GT- Horizontal gene transfer can be described as the transfer of genetic
information between two independent organisms.
2. VERTICAL GT- Vertical gene transfer is the transfer of genetic information from parent
to progeny. Germline, Live birth, Patrilineal, Aposymbiotic.

4. DNA transfer by natural methods:-
1. Conjugation
2. Bacterial transformation
3. Retroviral transduction
4. Agrobacterium mediated transfer
DNA TRANSFER BY ARTIFICIAL
METHODS:-
Physical methods-
1. Microinjection
2. Biolistics transformation
Chemical methods-
1. DNA transfer by calcium phosphate
method
2. Liposome mediated transfer
Electrical methods-
1. Electroporation

5. Horizontal gene transfer (Lateral gene transfer):-
The transmission of DNA (deoxyribonucleic acid) between different genomes is referred to
as horizontal gene transfer, sometimes known as lateral gene transfer. Between distinct
species, such as prokaryotes and eukaryotes , and between the three DNA-containing
organelles of eukaryotes—the nucleus, the mitochondrion, and the chloroplast—
horizontal gene transfer is known to happen. Vertical gene transfer, or the passing of genetic
material from parents to children during reproduction, is distinct from the acquisition of
DNA by horizontal gene transfer. Gene transfer in bacteria was studied by Griffith in 1928,
there are the following types of gene transfer mechanism.
Mechanism-
1. Transformation
2. Transduction
3. Conjugation
4. Transposon transfer
5. Fusion of cells

6. Gene transfer in prokaryotes-
Transformation
Transduction
Conjugation
Archaeal DNA transfer
Gene transfer in eukaryotes-
Organelle to nuclear genome
Organelle to organelle
Virus to plants
Bacteria to fungi
Bacteria to plants
Bacteria to animals
Endosymbiont to insects and nematodes
Plant to plant
Plant to animals
Plant to fungus
Fungi to insects
Fungi to fungi
Animal to animal
Animal to bacteria
Human to protozoa

7. TRANSFORMATION:-
The genetic alteration of a cell resulting from the introduction, uptake and expression of
foreign genetic material (DNA) in molecular biology. This can be done to Bacteria, Fungi,
Plants, and Animal cells.
Transformation principle was demonstrated
in 1944 by Oswald Avery, Colin MacLeod,
and Maclyn McCarty, who showed gene
transfer in Streptococcus pneumoniae was
pure DNA. Avery, Macleod and McCarty
call the uptake and incorporation of DNA by
bacteria transformation. A few bacteria, such
as Neisseria gonorrhoeae, Neisseria
meningitidis, Hemophilus influenzae,
Legionella pneomophila, Streptococcus
pneumoniae, and Helicobacter pylori tend to
be naturally competent and transformable.

8. Bacteria – transformation refers to a genetic
change brought about by picking up naked
strands of DNA and expressing it. –
Competence refers to the state of being able
to take up DNA. – Two different forms of
competence should be distinguished, natural
and artificial. The process of gene transfer
by transformation doesn’t require a living
donor cell but only requires the presence of
persistent DNA in the environment.
The factors that regulate natural competence
vary between various genera. Transformed
bacteria used as host cell in cloning
procedures, in DNA linkage studies,
generation of Cdna libraries, express large
amounts of proteins and enzyme.

9. CONJUGATION:-
Bacterial conjugation was discovered by Lederberg And Tatum in1946 in Esch.coliK12
strains. During conjugation , DNA is transferred from one bacterium to another. After the
donor cell pulls itself close to the recipient using a structure called a pilus, DNA is
transferred between cells. In most cases, this DNA is in the form of a plasmid. Donor cells
typically act as donors because they have a chunk of DNA called the fertility factor (or F
factor). This chunk of DNA codes for the proteins that make up the sex pilus. It also
contains a special site where DNA transfer during conjugation begins. Conjugation is
encoded by plasmids or transposons.
Conjugation are of different types:-
1. F+ conjugation
2. Hfr conjugation
3. Resistant plasmid conjugation
4. Sexduction

10. Conjugation steps-
Step 1:The pilus enables direct contact
between the donor and the recipient cells.
Step 2: Because the F-plasmid consists
of a double stranded DNA molecule
forming a circular structure, i.e., it is
attached on both ends, an enzyme
(relaxase, or relaxosome when it forms a
complex with other proteins) nicks one
of the two DNA strands of the F plasmid
and this strand (also called T-strand) is
transferred to the recipient cell.

11. Step 3: Donor cell and the
recipient cell, both containing
single-stranded DNA, replicate it
and thus end up forming a double-
stranded F-plasmid identical to the
original F-plasmid. (see below),
the old recipient cell is now a
donor cell with the F-plasmid and
the ability to form pili, just as the
original donor cell was. Now both
cells are donors or F+.

12. TRANSDUCTION:-
Transduction involves the transfer of a DNA fragment from one bacterium to another by a
bacteriophage. Bacteriophages, also known as phages, are viruses that infect and replicate
only in bacterial cells. They are ubiquitous in the environment and are recognized as the
most abundant biological agent on earth. They are extremely diverse in size, morphology,
and genomic organization.

13. There are two forms of
transduction: generalized
transduction(LYTIC PHAGE)
and specialized transduction
(LYSOGENIC PHAGE)
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 generation. The lytic cycle
leads to production of new
phage which is released by lysis
of host.

14. AGROBACTERIUM
MEDIATED TRANSFERS:-
Agrobacterium is a genus of Gram-negative bacteria established by H. J. Conn that uses
horizontal gene transfer to cause tumors in plants
Agrobacterium is a phytopathogen that infects plants through wound sites, causing
crown gall disease, and is one of the most popular plant transformation tools used in
agriculture to date.
Agrobacterium tumefaciens harboring the tumor-inducing (Ti) plasmid induces Crown
galls on stems, roots and crowns of numerous dicot angiosperm species and some
gymnosperms. The neoplastic tumor-like cell growth is induced by expression of the
oncogenes residing in the transferred-DNA (T-DNA) transported from these bacteria
into the plant nucleus and integrated into the plant genome.

15. Essential component of T-dna-
1. The first essential component is the T-DNA, defined by conserved 25-base pair
imperfect repeats at the ends of the T-region called border sequences.
2. The second is the virulence (vir) region, which is composed of at least seven major
loci (virA, virB, virC, virD, virE, virF, and virG) encoding components of the bacterial
protein machinery mediating T-DNA processing and transfer.
Major steps of the Agrobacterium tumefaciens-mediated gene transfer process:-
(1) Attachment of A. tumefaciens to the plant cells.
(2) Sensing plant signals by A. tumefaciens and regulation of virulence genes in
bacteria following transduction of the sensed signals.
(3) Generation and transport of T-DNA and virulence proteins from the bacterial cells
into plant cells.
(4) Nuclear import of T-DNA and effector proteins in the plant cells.
(5) T-DNA integration and expression in the plant genome.

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