Wednesday, 21 January 2015

Five Things You Should Know if You Want to Participate in the Junk DNA Debate

In the last few years, special creationists in our community have gradually become aware that one of the  most compelling lines of evidence for common descent comes from molecular biology and genomics. Their attempts to explain this evidence away as I have shown elsewhere betray a considerable lack of understanding of even the basic facts, and on this fact alone can be readily dismissed. In addition, the fact that at least two-thirds of our genome is junk poses another insuperable problem for special creationists who have to ask why an intelligent designer would create a genome that is anything but perfect, and leads to genetic disease. (Needless to say, the problem vanishes when we recognise the evolutionary origins of our genome).

In 2013, biochemist Larry Moran posted a list of five items that anyone wanting to weigh in on the junk DNA question needs to understand and satisfactorily answer before being able to have their assertions that junk DNA does not exist even considered, let alone taken seriously:
  1. Genetic Load: Every newborn human baby has about 100 mutations not found in either parent. If most of our genome contained functional sequence information, then this would be an intolerable genetic load. Only a small percentage of our genome can contain important sequence information suggesting strongly that most of our genome is junk.
  2. C-Value Paradox: A comparison of genomes from closely related species shows that genome size can vary by a factor of ten or more. The only reasonable explanation is that most of the DNA in the larger genomes is junk.
  3. Modern Evolutionary Theory: Nothing in biology makes sense except in the light of population genetics. The modern understanding of evolution is perfectly consistent with the presence of large amounts of junk DNA in a genome.
  4. Pseudogenes and broken genes are junk: More than half of our genomes consists of pseudogenes, including broken transposons and bits and pieces of transposons. A few may have secondarily acquired a function but, to a first approximation, broken genes are junk.
  5. Most of the genome is not conserved: Most of the DNA sequences in large genomes is not conserved. These sequences diverge at a rate consistent with fixation of neutral alleles by random genetic drift. This strongly suggests that it does not have a function although one can't rule out some unknown function that doesn't depend on sequence.
Closely related to this is of course the ENCODE debacle. For more on that, follow this link.