Indeed, every bit of your being, every gene in your genome, every base pair in your DNA, is no longer extant.
Or is it?
Well, scientists have recently taken a bit of DNA called Col2A1, gleaned from the extinct Tasmanian tiger (Thylacinus cynocephalus), extracted from 100 year-old museum samples, put that DNA in a mouse, and got it to function.
The DNA is a transcriptional enhancer. This is a bit of “non-coding” DNA that has an effect on the expression of other DNA. In this experiment, this worked. Extinct DNA of this type has been expressed in vitro, but this is the virst time in vivo.
(a) Young male thylacine in Hobart Zoo in 1928, photograph (Q4437). (b) One of the preserved pouch young specimens (head length 34 mm) from which DNA was extracted, from the Museum Victoria collection. (c-f) The skull of the thylacine (c,e) compared with that of the domestic dog Canis canis (d,f). The morphology of the head shows remarkable convergent evolution. However, there are some differences: in marsupials, the lacrymal extends outside the orbit and the angle of the dentary is medially inflected (c). The thylacine palatine has the vacuities characteristic of marsupial skulls (e). The teeth also show striking convergent evolution but the muzzle of the thylacine is quite narrow compared to that of the dog (e,f). Scale bar = 5cm.
In particular, the effects of the trancriptional enhancer was observed by watching the effects on a “reporter gene” (a gene that would be affected by it). The reporter gene predicted pretty much as expected. During the development of the mouse embryo, the reporter gene was expressed where and when, and roughly in the amount (though this varied) as expected.
The authors conclude, “Our method using transgenesis can be used to explore the function of regulatory and protein-coding sequences obtained from any extinct species in an in vivo model system, providing important insights into gene evolution and diversity.”
This assumes that the word “function” is used very carefully, of course. The exact effects of a gene may depend on context to the extent that one bit of DNA may function in one organism in a different way than other organism to the extent that we would normally assign the two outcomes to two different functions. It is that kind of context based functionality that makes genes a) really interesting and b) able to do so much work despite the fact that there are actually not that many different kinds of genes.
Pask, A.J., Behringer, R.R., Renfree, M.B., Svensson, E.I. (2008). Resurrection of DNA Function In Vivo from an Extinct Genome. PLoS ONE, 3(5), e2240. DOI: 10.1371/journal.pone.0002240