Molecular Genetics

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In addition to the changes that genomes undergo due to mutations arising from unrepaired damage to DNA and replication errors, genomes change by a variety of other mechanisms, loosely classified as rearragements.

• Two types of rearrangements can be distinguished mechanistically:
  • In site-specific recombination, specific target sequences on each of two DNA segments are sites of strand exchange, resulting in inversions, deletions and insertions.
  • In transposition, a specific target sequence on one DNA seqment is the site of initiation of transfer to another DNA sequence by one of several distinct mechanisms. Some transposition events require the progress of the replication fork.
• Some rearrangements play important roles in the life cycle of the organism and are called programmed rearrangements.
• Rearrangements are often called illegitimate recombination to distinguish them from general or homologous recombination in which exchanges occur between homologous DNA sequences.