Genome complexity: mutations self-directed? (Introduction)

by David Turell , Friday, May 06, 2016, 15:22 (3124 days ago) @ David Turell

That is what is suggested by this article:-http://toddcwood.blogspot.ca/2016/05/research-week-directed-mutations.html- " Pinto et al. looked at an enzyme called APOBEC3G, that is part of a family of genes in human and ape genomes that deaminate cytosines. "Deaminating cytosine" is a sort of "directed mutation," because that chemical reaction changes the sequence of DNA at a single nucleotide position. - "APOBEC enzymes are thought to defend human cells against viruses by mutating them so they don't work any more. Pinto et al. wondered if there might be evidence of APOBEC enzymes acting on human and ape genomes as well. Think of it as a sort of "collateral damage" in the war against viruses. In their survey, they found eight thousand unique clusters of mutations that look like APOBEC mutations in the human genome, as well as the genomes of Neandertal and Denisovans. They found almost a half million that were unique to the entire genus Homo. The fact that these mutations are unique to these different forms of human indicates that this enzyme has indeed altered human genome sequences since creation. And that's just one version of an enzyme family that has multiple variants in the human genome.-" Now, we have to put this into perspective. APOBEC doesn't account for all variations in the human genome, or even most of the variations. It doesn't explain why the human genome is nearly identical to other ape genomes. All we get from this research is one example of how an enzyme really could alter a human genome sequence at one nucleotide position. That's pretty exciting stuff, though, and it greatly alleviates my unease about "directed mutations." They really can happen."-Comment: this is part of the immune system defenses. We develop a system of memory cells (T cells, B cells in lymphocytes) with modified DNA which gives us the output of antibodies against infections of all sorts and most of thee memories last a lifetime. This is a purposeful mechanism against infections, resembles epigenetics but isn't as a valid part of the initial genome.