History

History of junk DNA

The history of junk DNA begins in the 1940s with a discussion about mutation load, or genetic load. The leading thinkers were J.B.S. Haldane and Hermann Muller who was awarded the Nobel Prize in 1946 for his work on mutations. They, and others, realized that given the rate of mutation in humans, the amount of the genome that could be susceptible to deleterious mutations had to be only a fraction of the total otherwise our species would go extinct.

By the early 1960s, it seemed likely that the human genome could only contain about 30,000 genes based on mutation load. The rest had to be relatively inert to the deleterious consequences. of mutation.

At about the same time, more and more data on genome sizes in different species revealed that there was a wide range of sizes, even within the same genus. There didn't seem to be any correlation between genome size and the complexity of a species. This mystery was called the C-Value Paradox where "C-value" refers to the genome size.

The technique of reassociation kinetics gave rise to C₀t analysis which showed that large eukaryotic genomes contained substantial amounts of repetitive DNA. In fact, most of the differences in genome size could be explained by differences in the amount of repetitive DNA. It looked like most of the functional DNA elements were confined to the unique sequence DNA that formed a smaller percentage of the genome. If the repetitive DNA was nonfunctional, then this was in line with mutation load arguments and helped resolve the C-Value Paradox.