More problematic is the reality that the human genome is still a vast catalogue of the unknown and scarcely known. The Human Genome Project’s most startling finding was that human genes, as currently defined, make up less than 2 percent of all the DNA on the genome, and that the total number of genes is relatively small. Scientists had predicted there might be 80,000 to 140,000 human genes, but the current tally is fewer than 25,000 — as one scientific paper put it, somewhere between that of a chicken and a grape. The remaining 98 percent of our DNA, once dismissed as “junk DNA,” is now taken more seriously. Researchers have focused on introns, in the gaps between the coding segments of genes, which may play a crucial role in regulating gene expression, by switching them on and off in response to environmental stimuli. Gene regulation, whether by introns or by regulator genes, forms one aspect of the burgeoning field of epigenetics, which concerns itself with the process of differential gene expression. In a classic study published in 2004, biologists at McGill University in Montreal identified a regulatory sequence in rat pups that lowered stress hormone production when the mother groomed them; their production of the hormone stayed low throughout their lives. Moreover, the researchers could adjust the gene in healthy adults to increase their stress, and in agitated adults to lower it. Though not their intention, the study provided the genetic evidence to prove Freud right: what happens in childhood has a lasting, though theoretically reversible, biological effect on adult behaviour.
more from Mark Czarnecki at The Walrus here.