As we have heard in the summaries of the human ENCODE project, 80 per cent of ju

Question

As we have heard in the summaries of the human ENCODE project, 80 per cent of junk DNA appears to have an essential function. Many fish have a genome with only one tenth the size of a usual vertebrate genome. Why can fish have 1/10th of junk DNA and be still fully functional? What has a frog more than a fish has? I'm especially interested if we can see the difference somewhere, complexity of physiology or anatomy, or such.

Jap. puffer fish genome: 390 Megabases, 47,800-49,000 genes (UniProt)

Medaka genome: 690 Megabases, 24,600 genes

Clawed frog: 1,500 Megabases, 23,500 genes

Explanation / Answer

Genome size is a poor indicator of an organism's complexity (already an ill-defined term). We cannot assume by any means that a larger genome corresponds to a more "complex" organism. There are some plants whose genomes are larger than most mammals, and indeed the largest eukaryotic genome (at least as of 2010) is the plant Paris japonica, weighing in at 1C = 152.23 pg (compared to Homo sapiens at 1C = 3 pg). Anecdotally, in my previous research lab I discussed with a colleague a fungal species whose genome size differed by orders of magnitude between different individuals of that species.

It should never surprise you to see an organism with a larger genome size than what you may consider to be a more complex organism.

Related Questions

Navigate

• Browse (All)
• Browse A
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.