C-value

The C-value Paradox

By the beginning of the 1960s, scientists knew that different species had very different amounts of DNA in their genome. Even species within the same genus could have substantially different C-values. This gave rise to the C-Value Paradox because there wasn't any easy way of explaining the data.

This changed with the discovery that the differences were mostly due to differences in the amount of repetitive DNA and that came at a time when the neutral theory of evolution was being developed. It was no longer seemed necessary to postulate that genome size was adaptive and it didn't seem reasonable that all the repetitive DNA had a function.

The idea that most of eukaryotic genomes were junk seemed like a good way of resolving the C-Value Paradox and it was consistent with the genetic load arguments dating back to the 1940s. Junk DNA had a measure of explanatory power that no other hypothesis possessed and it soon became the dominant model among those who thought about such things.

Later on, it became clear that much of this repetitive DNA consisted of fossil transposons that were no longer active and this reinforced the idea that the spread of transposons, and their subsequent inactivation, accounted for junk DNA.

The C-Value Paradox is no longer a paradox. We now use the term C-Value Enigma to refer to the problem of accounting for the origin of junk DNA in different species. However, even that term is falling out of use since we have good models to explain the origin of junk DNA.