Here are five things you should know if you want to engage in a legitimate scientific discussion about the amount of junk DNA in a genome.
- 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.
- 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.
- 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.
- 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.
- 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.
If you want to argue against junk DNA then you need to refute or rationalize all five of these observations.
This post originally appeared on Sandwalk on July 4, 2013 [Five Things You Should Know if You Want to Participate in the Junk DNA Debate]
