Why is human genome > pufferfish genome?
[ANIMAL GENOMES]
More retrotransposons are in the
human genome. They are located
within the introns, making the introns
in the human genome larger.
Why is maize genome > sorghum genome
[PLANT GENOME}
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?
Hypothesis 1: Alternative splicing
Can make multiple proteins from a single gene & mRNA transcript
While many organisms have introns,
not all organisms have alternative
splicing. Therefore this hypothesis
cannot explain the presence of all
introns
Hypothesis 2: mobile group II introns
Mechanism
Our genome's splicing machinery and
mobile group II self-splicing are very
similar. They likely share a common
ancestor
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
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.
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