On 8/21/24 20:22, John Harshman wrote:
On 8/21/24 7:43 PM, John Harshman wrote:
On 8/21/24 12:51 PM, RonO wrote:
https://www.nature.com/articles/s41586-024-07830-1
paywalled, but Science news article:
https://www.science.org/content/article/odd-fish-has-30-times-much-dna-humans-new-record-animals
They have just identified the new largest animal genome, but unlike
amphibians that duplicated their whole genomes over and over to
create their large genomes this lobe-finned fish (a species of
lungfish) enlarged it's genome by failing to regulate the
multiplication of transposons. It has a 91 billion base-pair
genome, but still only as many genes as related lobe-finned fish
(lobe-finned fish gave rise to tetrapods). It has roughly the same
number of genes that humans have, but it's genome is 30 times
larger. Allowing transposons to run rampant has increased it's
genome size with copies of transposons by about 3 billion base-pairs
every 10 million years.
Transposons are parasitic bits of DNA that can replicate and move
from place to place in the genome. Because of their parasitic nature
they have been lumped into junk DNA, but they often do have
functional genes, and take their own transcription regulatory
sequences with them when the hop around the genome, so they have some
function, but it isn't geared to helping out the host. They just use
the host cells to keep replicating more copies of themselves.
Jumping into genes causes genetic diseases and jumping around genes
can cause differential regulation of the surrounding genes, so they
cause insertion mutations that do affect the organism, but like other
mutations, most of the mutations are benign, some of them are bad,
and a few of them may do some interesting things. At this time for
this lungfish probably nearly all new transposition events are likely
messing up existing transposon sequence. About 90% of the genome
seems to be transposon sequence at this time, but my guess is that
most of the remaining 90% is just old transposon sequence that has
been mutated to the extent that they can't recognize the fragments as
once being transposons.
Ron Okimoto
That's Lepidosiren paradoxa. It's been known for a long time that it
has a huge genome, and that the other lungfish also have huge genomes.
In fact, it appears that Protopterus aethyopicus has an even bigger
one. So no huge surprise here, just greater detail on *why* it has a
huge genome.
Check out the animal genome size database:
http://www.genomesize.com/results.php?page=1
Ah, I see it's actually the largest animal genome *sequenced so far*. It
may be the 4th or 5th largest, and possibly the second-largest to get
that way without polyploidy.
So it is interesting how you can look at a macroscopic organism
and not really tell very well - this has a long (base pairs)
genome and this one does not.
So exclude the slime molds and do not call them something like ultra-polyploidal.
Are there some other organisms that have really long genomes
besides some lobe finned fish and some lungfish and some frogs?
What is the shortest frog genome? Are there any frogs with
genomes shorter than humans or even chickens? Which ones are
those?
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