Like René Magritte's painting of a pipe entitled "Ceci n'est pas une pipe" — or "This is not a pipe" — what is called "the human genome" today in fact "doesn't exist," says Penn State Professor Ken Weiss at The Mermaid's Tale blog. The human genome is no more real than "the chair" or "the dog," he adds. Paraphrasing Plato, Weiss says that while we know dogs and chairs exist, they are only examples of such. And so it is with the human genome.
"[The human genome] is not from one person, not even one copy from one person's two. It's a composite from several donors," Weiss says. "It's not a 'normal' genome, because while we believe the sequenced individuals were healthy at the time they bled for the cause, they won't be healthy forever. … Worse, 'the' genome keeps changing! We are now in version 19, released in 2009."
And if the human genome doesn't exist, he adds, nor do individual genes. "We use 'the' HG [human genome] sequence as a way of referring to a standardized set of nucleotide locations along the chromosomes in the individuals who were sequenced," Weiss says. "Each of us varies from that sequence in millions of places (in each copy that we carry)."
The reference sequence is useful, Weiss says, but it's important to remember that no one has that exact sequence. We are all "type specimens," he adds — and so are our genomes.