Transposons and Genome Mutation

Transposons

• Transposons are randomly distributed across the genome, often in regions where homology permits recombination.
• The original transposon sequence remains after transposition; it's copied, transcribed, and pasted into a new location.
• Transposition adds locations for the sequence and propagates it throughout the genome.
• Transposition is an error-prone process with no proofreading during reverse transcription, leading to a high mutation rate.
• Transposons insert themselves near suitable promoters.
• Approximately 40% of our genome comprises remnants of transposons, specifically LINEs (long interspersed nucleotide elements), SINEs (short interspersed nucleotide elements), and LTR retrotransposons (similar to SINEs).

Impact on Host Genome

• Most individuals have LINEs that are still capable of transposition.
• Active transposition is detrimental to the host genome.
• Chromosomal rearrangements become more likely when chromosomes contain multiple copies of the same sequence.
• Recombination between dispersed repeats leads to inversions, deletions, and duplications.

Mechanisms of Mutation

• Transposons can cause mutations by:
  • Directly disrupting genes when they insert, leading to loss-of-function mutations.
  • Facilitating unequal recombination between different copies in the host genome.
• Many known loss-of-function mutations are caused by transposon insertions.

Transposition Process

• The excised transposon forms a circular product.
• This circular form then re-integrates into the genome at a new location.
• Re-integration can disrupt genes near the insertion site.