Mobile elements

Why do genome sizes differ?
1. Retrotransposons
  1. Mechanism
  2. Why is human genome > pufferfish genome? [ANIMAL GENOMES]
    1. More retrotransposons are in the human genome. They are located within the introns, making the introns in the human genome larger.
  3. Why is maize genome > sorghum genome [PLANT GENOME}
    1. More retrotransposons are in the maize geome. They are located between the genes making the physical space between genes larger in the maize genome.
Why are there introns?
1. Hypothesis 1: Alternative splicing
  1. Can make multiple proteins from a single gene & mRNA transcript
  2. While many organisms have introns, not all organisms have alternative splicing. Therefore this hypothesis cannot explain the presence of all introns
2. Hypothesis 2: mobile group II introns
  1. Mechanism
    1. Our genome's splicing machinery and mobile group II self-splicing are very similar. They likely share a common ancestor
  2. 1. Very early on in plants and animals, mobile introns evolved and spread throughout animal and plant genomes. They are neutral since the self-splice out
    1. 2. Mobile group II introns will eventually acquire mutations that break their self-splicing machinery. Now the mobile group II introns are deleterious because they prevent the gene their inserted in from being translated and expressed properly.
      1. 3. Plants and animals can solve this problem by finding a way to splice the mobile group II introns themselves by supplying their own splicing machinery
        4. Over time the dead mobile group II introns will acquire enough mutations so that they now look like the 'regular' introns we see today. They are no longer mobile and become unrecognizable as mobile group II introns
        5. Some introns (but not all) evolve to regulate genes or enable alternative splicing

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Mobile elements

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