(June 5, 2024 at 1:33 pm)Lucian Wrote: Apparently the largest know genome size in the world now belongs to a variety of fern Tmesipteris oblanceolata. Whilst humans have 3.1 billion base pairs in our DNA, this plant has 160 billion!
It seems to add to the power of the "onion test" that basically argues that if someone wants to claim that most or all of the human genome is functional and necessary, they need to explain the same in these other genomes of what seem more simple organisms. If they can't do that, for these larger genomes, why assume that all the human genome or other animal's genomes must be largely necessary, and the product of good coding.
While I can't speak to this particular example it has been shown that many of these "simpler" organisms are any but. For example, most amphibians have larger genomes because they have to code for several suites of proteins for living in all sorts of different conditions, on land, in water, and at various different stages of life. Because they don't maintain a constant internal temperature, proteins that function at 5 C may be useless at 15 C and vice versa. We avoid all those shenanigans by maintaining a very consistent internal environment and having one set of genes that works really well under those conditions.
That said, a lot of our genome is nonfunctional except possibly as the canvas that evolution spatters its paint. We know this because we can compare the background mutation rates in the nonfunctional portions to determine if a portion of the genome is, or may have been at some point, active in some way. Mutations in nonfunctional segments of the genome don't do anything, so all you get is a random walk type of change. By contrast, active segments of the genome rapidly evolve toward an optimal configuration and then become much more conserved. You see a lot more mutation preserved during the optimization followed by a lot less once it's as good as it's going to get.
