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From: John Harshman <john.harshman@gmail.com>
Newsgroups: talk.origins
Subject: Re: Largest animal genome 91 billion base-pairs.
Date: Wed, 21 Aug 2024 20:22:07 -0700
Organization: University of Ediacara
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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.