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Therefore, a group of microorganisms may respond to a C source but go undetected using this technique.
Additionally, this technique is biased towards identifying microorganisms with A- and T-rich genomes.
Ever since it was shown that neurogenesis takes place in hippocampus of the adult brain (see ARF related news story), an outstanding question has been whether or not cortical neurons can be replenished in adults.
To tackle this question, the authors isolated neuronal and non-neuronal nuclei from cerebral cortex tissue samples.
Because this test can be used retrospectively, unlike many of the current methods used to detect cell proliferation, and because it does not require the ingestion of a radioactive or chemical tracer, the method can be readily applied to both in vivo and postmortem samples of human tissues.
Because atmospheric C14 levels are falling relatively quickly, the method will decrease in sensitivity with time, so the period during which it will be useful is limited and people born around the time of the nuclear tests will remain the most suited for study.Indeed, when Spalding and colleagues examined samples that dated prior to or after the proliferation of atmospheric nuclear tests, they found that the C14 content in the DNA correlated with the predicted atmospheric C14 at the time the DNA would have been synthesized.Next, examining samples from single individuals born after the test ban treaty went into effect, the authors found that the C14 content in DNA isolated from the cerebellum, cortex and intestine were, as would be expected, the same age.Because of its extremely long half-life (over 5,000 years), carbon 14 content has typically been used to date only very old artifacts or fossils.The method has traditionally failed to resolve dates of samples that differ in age by less than a few hundred years—accurate enough perhaps to date the youngest and oldest parts of the most ancient redwood trees, but not to tell how many newborn cells might be present in the human brain.