Question

QUESTION 36 some specific detail about what they have, how they get around, etc. What are transposons? Incude in your answer what types Include a comparison of LINES and SINES. TT T Arial 3 (12pt) Path: P Words o

Answer 1

Transposons are the mobile genetic elements that have the ability to shift position in the genome by employing cycles of transient breakage and subsequent fusion of double-stranded DNA.

Transposons are found to encode a special protein named as transposase which catalyses the process of transposition. Transposons are particular to different groups of organisms. They constitute a fairly accountable fraction of genome of organisms like fungi, bacteria, plants, animals and humans. Transposons have had a major impact on changing or altering the genetic composition of organisms.

The Significance of Transposable Elements:

• Transposons may change the structural and functional characteristics of genome by changing their position in the genome.
• Transposable elements cause mutation by insertion, deletion, etc.
• Transposons make positive contribution in evolution as they have tremendous impact on the alteration of genetic organisation of organisms.
• They are useful as cloning vectors also, in gene cloning. For example, P-elements are frequently used as vector for introducing transgenes into Drosophila.
• Transposons may also be used as genetic markers while mapping the genomes.
• Transposon-mediated gene tagging is done for searching and isolation of a particular gene.

Different transposons may change their sites by following different transposition mechanisms.On the basis of their transposition mechanism, transposons may be categorized into following types:

• Cut-and-Paste Transposons
• Replicative Transposons
• Retro Elements:

Transposable Elements in Prokaryotes

Bacterial transposable elements are of the following types:

• Insertion Sequences or IS Elements
• Prokaryotic Transposon Elemen

Transposable Elements in Eukaryotes

• Transposons in Maize​​​​​​​​​​​​​​
  • Ac-Ds system
  • spm (suppressor mutator) system,
  • dt (dotted) system,
  • Mu (Mutator) system
• ​​​​​​​Transposons in Drosophila
  • ​​​​​​​P-elements
  • Copia-elements
  • FB Elements
• ​​​​​​​Transposons in Humans
  • ​​​​​​​ SINEs (Short Interspersed Elements): short interspersed elements; originally defined by their interspersed nature and length (75–500bp), but also further characterized by their RNA polymerase III transcription.
  • LINEs (Long Interspersed Elements): Long interspersed elements; full-length elements are ~6kb in length, contain an internal promoter for Polymerase II, two ORFs, and end in a polyA-tail.

SINEs are short interspersed retrotransposable elements and LINEs long interspersed retrotransposable elements, that invade new genomic sites using RNA intermediates. SINEs and LINEs are found in almost all eukaryotes (although not in Saccharomyces cerevisiae) and together account for at least 34% of the human genome. The noncoding SINEs depend on reverse transcriptase and endonuclease functions encoded by partner LINEs. With the completion of many genome sequences, the database of SINEs and LINEs has taken a great leap forward. Current work ranges from the biochemistry of reverse transcription and integration invitro, target site selection in vivo, nucleocytoplasmic transport of the RNA and ribonucleoprotein intermediates, and mechanisms of genomic turnover. Two particularly exciting new ideas are that SINEs may help cells survive physiological stress, and that the evolution of SINEs and LINEs has been shaped by the forces of RNA interference. Taken together, these studies promise to explain the birth and death of SINEs and LINEs, and the contribution of these repetitive sequence families to the evolution of genomes.