Transposable elements, also called jumping genes, are DNA sequences that can move within a genome. They are found in all organisms and make up a large percentage of some genomes, such as 45% of the human genome. Barbara McClintock discovered transposons in maize in 1948. There are two main types - retrotransposons that move via an RNA intermediate and DNA transposons that move directly as DNA. Transposition can occur through replicative or non-replicative mechanisms. Transposons can have mutagenic effects but also have applications in genetic engineering and gene discovery.

1. Sahar Zaidi
14- MBT -14

2. CONTENTS
•Introduction
•History
•General Characteristics
•Mechanism
•Types of transposons
•Transposition
•Transposable elements in bacteria and humans
•Mutagenic effects
•Applications
•Conclusion

3. INTRODUCTION
JUMPING GENES:- are moderately repetitive DNA
sequences interspersed at multiple sites through out the
genome that can move or jump from one location in the
genome to another.
These sequences are found in all organisms.
45% of human genome.
90% of maize genome.

4. HISTORY
Barbara Mc Clintock discovered transposable
elements in 1948 in maize for which she was
awarded noble prize.

5. GENERAL CHARACTERISTICS
•These elements encode enzymes that can insert their
sequence into new sites.
•Terminal inverted repeats are
generally present at the ends.
•They generate direct repeats at
the point of insertion.

6. GENERAL MECHANISM

7. TYPES OF TRANSPOSONS
1. Retrotransposons
2. DNA transposons.

8. RETROTRANSPOSONS
Also called as CLASS 1 elements.
Transpose through RNA intermediate, are transcribed
from transposable element and are then copied back
by reverse transcriptase.
Retrotransposons are more common in eukaryotes.

9. DNA TRANSPOSONS
Are CLASS 2 elements.
These transpose to new sites directly as DNA.
These are more common in prokaryotes.

11. TRANSPOSITION
The process by which these sequences are
copied and inserted is called as transposition.
On the basis of mechanism involved.
1. Replicative transposition.
2. Non replicative transposition.

12. REPLICATIVE TRANSPOSITION.
In this type of transposition, a
new copy of transposable
element is introduced at a new
site, old copy remains behind at
original site.

13. NON REPLICATIVE TRANSPOSITION
In this type of transposition, the
transposable element excises from
old site and inserts at a new site.

14. TRANSPOSABLE ELEMENTS IN BACTERIA
1.Insertion sequences (IS).
2.Composite transposons.
3.Non composite transposons.
They generally use non-replicative transposition.

15. INSERTION SEQUENCES
•They are the smallest and simplest transposable
elements as they carry only the genetic information
that is needed to sponsor their own transposition.
•They are denoted by IS
followed by a number.

16. COMPOSITE TRANSPOSONS
• Transposons that carry genes (like antibiotic
resistance) in addition to those coding for
transposition.
• They have a central region flanked by an IS
element at each end.
• A composite transposon may transpose as a
unit , but an active IS element at either end
may also transpose independently.
• These are named Tn followed by a number.

17. NON COMPOSITE TRANSPOSONS
•These transposable elements lack
IS and are bracketed by short
inverted repeats.
•Carry genetic information for
transposase and resolvase plus a
gene that encodes for enzyme
lactamase that provides
resistance to ampicillin.

18. TRANSPOSONS IN HUMANS
98% of transposable elements in humans are
retrotransposons.
1. LINEs (long interspersed nuclear elements)
2. SINEs (short interspersed nuclear elements)

19. LINES
Represents 17% of human genome.
LINEs are retrotranspositionally active elements.
 L1 LINE family are most commonly in human genome.
 They are approximately 6kb in length.
 The consensus sequence contains 2 large reading frames
• ORF1 encodes an RNA binding protein.
• ORF2 encodes protein having both endonuclease and
reverse transcriptase activity.

20. SINES
These represent 11% of human genome
•SINES are dependent on LINES for retrotransposition.
•These are 100 to 400bp long.
•Most common SINES in human genome are Alu elements
•Alu are 300bp long and 1 million copies per cell are present.

21. MUTAGENIC EFFECTS
• TEs are mutagens, they can damage the genome of their host cell in different
ways:-
• a transposon or a retroposon that inserts itself into a functional gene will
most likely disable that gene;
• after a DNA transposon leaves a gene, the resulting gap will probably not be
repaired correctly;
• multiple copies of the same sequence, such as Alu sequences can hinder
precise chromosomal pairing during mitosis and meiosis , resulting in
unequal crossovers one of the main reasons for chromosome duplication.
• Diseases that are often caused by TEs include haemophilia, severe combined
immunodeficiency , predisposition to cancer, and Duchenne muscular
dystrophy LINE1 (L1) TEs that land on the human Factor VIII caused
haemophilia and insertion of L1 into APC gene caused colon cancer and this
confirms that the TEs play an important role for disease development.

22. USES OF TRANSPOSONS
Transposable elements are nature`s tool of
genetic engineering.
• Transformation vectors for transferring genes.
• Also drug resistance genes encoded by many transposons
are useful in the development of plasmid as cloning
vehicles.
• Insertional mutagenesis.
The Sleeping Beauty transposon system is a synthetic DNA
transposon designed to introduce precisely defined DNA
sequences into the chromosomes of vertebrate animals for
the purposes of introducing new traits and to discover new
genes and their functions.

23. CONCLUSION
•Early view of mobile elements as junk DNA or
completely selfish molecular parasites appears to
be premature. Rather, they probably have made
profound contributions to the evolution of higher
organisms by serving as the sites of
recombination, leading to the evolution of novel
genes and new controls on gene expressions.