I read reading New Scientist, and I found something new and cool to learn about: DNA reassociation.
It’s a technique for determining the number of different types of organisms in a given amount of material. What happens is that a chemical is added which causes the DNA double helix to “unzip,” leaving single strands of DNA. The single strands are mixed up with many other single strands of DNA, and the amount of time that it takes for the strands to find a match yields a rough estimate of how many distinct types of organisms are present in a given sample. The point of the actual article was to say that there are many more species of bacteria undergound than were previously thought. I just thought the DNA reassociation thing was much cooler.
When this technique was applied to soils in the late 1990s, it suggested that a gram of dirt contained about 16,000 species. But this estimate assumed that the populations of all the different species in the soil were roughly equal in size. So Gans and his colleagues have developed new equations to reanalyse the same DNA reassociation data but without this size assumption.
Their results reveal that there are a few very common species in soil but lots of rare species. “There is a very large number of low abundance species,” says Gans. So many rare species, in fact, that the estimate of bacterial biodiversity rises to one million species per gram of soil.
If you do an Internet search for “DNA reassociation” you’ll find lots of academic websites explaining the equations to describe rates of reassociation and how they relate to real world strand diversity in a given sample, but all of them (that I found) make an assumption about the size of the strand involved. I wonder how these new equations will alter the study of DNA reassociation kinetics?
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