In humans, we have a gene that at one time in our distant past, worked to manufacture vitamin C for us, but it is no longer functional, and now is among the pseudogenes we carry. Non-functional, yet still present.
So, out of curiosity, can anyone else suggest traits and features that we have lost, but still carry pseudogenes for?
By the way, dogs have a working copy of the vitamin C-producing genes.
Lousy lovable dogs…
There are thousands upon thousands (probably) of pseudogenes in humans. Most of these are thought to be retroviral in origin. At many points during evolution, retroviruses infected humans or human ancestors, got themselves integrated into the genome, and got lucky enough to go germline. This means that it made it to the sperm or eggs. It was propogated by human reproduction.
Some retroviruses do not de-integrate unless conditions turn sour. If conditions never turn sour, the retroviruses accumulate random mutations in their essential genes. Because their genes are never expressed, it is not a loss of fitness to mutate them. After a while, enough of the genes in the previous retrovirus become mutated such that the retrovirus cannot excise itself from the genome. At that point, it becomes a part of the genome padding.
Anyway, there are literally thousands of retrovirally derived sequences in the human genome. Only one retrovirally derived gene is expressed with a function in humans to the best of my knowledge. This is the gene syncytin, involved in placental morphogenesis, which was the env gene from the human endogenous retrovirus HERV-W.
It should be noted that some pseudogenes do not code for unused traits, but are pseudo-copies of genes we use. For instance, the two globin complexes (alpha and beta) each contain at least one pseudocopy of the standard alpha or beta-globin gene. These pseudogenes aren’t expressed, but at some time probably were shortly after the gene duplication.
LL
There is a vestigial genetic trace, thought to be originally used when men and women gathered food together. The only thing left is the belief among all humans that (the other gender) don’t know how to shop.
–Nott, who is of the rush-in-and-grab-one gender
There’s thousands of former smell receptor genes which are now psuedogenes. The one study I saw the results for estimated that about 70% of the original (proto-primate) smell receptors have been disabled in humans by being turned into pseudogenes. For the other great apes, this figure is about 50% and for the lower primates, the number is lower still.
BTW, most mammals have the vitamin C gene. Primates and guinea pigs are the exceptions, I believe.