“Junk” DNA Not so Junky
A recent report by researchers from the University of British Columbia (UBC) provides new evidence that non-coding DNA (typically referred to as “junk” DNA or “selfish” DNA) is not useless. Instead it appears to serve an essential function in complex cells.1
The DNA content of complex cells (cells that possess a nucleus and internal membrane-bound organelles and compartments) varies enormously (as much as 80,000 times) among protozoans, fungi, animals, and plants. The widely varying DNA content results from the presence of non-coding DNA. Non-coding, or “non-specific,” DNA can make up anywhere from 30% to nearly 100% of an organism’s total DNA content (genome).2
Those seeking to explain life as the outworking of strictly natural processes have suggested that non-coding DNA is produced randomly. Either it is “junk” carried along with functional genes simply because it is physically attached, or it is “selfish,” a type of functionless parasite in the organism’s genome.3-4 The “junk” or “selfish” DNA exemplifies the imperfection one would expect from random natural processes and is the preferred view among evolutionary biologists.
As far back as 1978, however, some researchers suggested that non-coding DNA may actually have a functional role. They developed a model in which the non-coding DNA determines the volume of a cell’s nucleus.5 As overall cell volume increases, the nuclear volume, and hence DNA content, too, must increase to give the cell’s nuclear contents room to communicate effectively with the cell’s cytoplasm (stuff outside the nucleus).
The UBC team has found experimental support for the usefulness of non-coding DNA in their study of cryptomonads (algae).6 The non-coding DNA appears to have kept the volume of the nucleus proportional to overall cell volume. Additionally, they found evidence refuting the “junk” or “selfish” model. A specialized cell part called the nucleomorph behaved opposite to what the naturalistic model predicts and exactly as the “purposeful” model predicts.
We still have much to learn about genome organization and non-coding DNA. Clearly, though, the more we uncover, the less likely the notion that an organism’s genome (including non-coding DNA) has been assembled by blind, chance processes, and the more likely it becomes that the genome is the work of an Intelligent Designer.
- Margaret J. Beaton and Thomas Cavalier-Smith, “Eukaryotic Non-Coding DNA is Functional: Evidence from the Differential Scaling of Cryptomonad Genomes,” Proceedings of the Royal Society of London B, 266 (1999): 2053-2059.
- Wen-Hsiung Li, Molecular Evolution, (Sunderland, Massachusetts: Sinauer Associates, Inc. Publishers, 1997): 379-401.
- W. Ford Doolittle and Carmen Sapienza, “Selfish Genes, The Phenotype Paradigm and Genome Evolution,” Nature, 284, (1980): 601-603.
- L. E. Orgel and F. H. C. Crick, “Selfish DNA: The Ultimate Parasite,” Nature, 284 (1980): 604-607.
- T. Cavalier-Smith, “Nuclear Volume Control by Nucleoskeletal DNA, Selection for Cell Volume and Cell Growth Rate, and the Solution of the DNA C-Value Paradox,” Journal of Cell Science 34, (1978): 247-278.
- Beaton and Cavalier-Smith: 2053-2059.