Like you were probably taught in school
At the Huffington Post, Microbiologist James Shapiro has been helping readers “see past Darwin,” to use James Barham’s term, for some time now. Here are two recent entries:
Take 2: (08/07/2012) Why Genetic Recombination Is Not Random, and How Cells Take Advantage of Non-randomness:
In the pre-DNA era, students were all taught that genetic change is random and accidental. Because the molecular details were inaccessible, this was the default assumption. But once we learned about DNA carrying hereditary information, we could research the details of how changes occur. We no longer needed to assume. We could investigate.
One of the main topics in molecular genetics has been the process of recombination between homologous chromosomes. This process makes it possible to construct genetic maps showing the relative positions of markers along the chromosomes.
Homologous recombination is not accidental. It is a required part of the special cell divisions called “meiosis” that that produce sperm and egg cells with only one copy of each chromosome. Without meiosis, sexual reproduction would not be possible as found today in higher organisms.
Legitimate and Illegitimate Recombination: Targeting Homologous Exchange for Multiple Adaptive Purposes:
“Legitimate recombination” was assumed to be reasonably uniform in the early days of genetics. That was the basis of constructing genetic maps. We now know homologous recombination can be used “illegitimately” (i.e. targeted either positively or negatively). I think the molecular studies are remarkable in uncovering a striking variety of ways cells have adapted homologous recombination for diverse purposes. As the recent mouse paper shows, we have only begun to scratch the surface of what promises to be a rich vein of cellular inventiveness.
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