In studies of the metallothionein gene in Drosophila we have found at
least five different duplications of Mtn in European and North American
populations, which suggests to me that duplications are relatively common
occurrences. In Europe these duplications seem to be favored by
selection because in some samples they are present in up to 50% of
chromosomes.
In samples from Africa, on the other hand, we never found an Mtn
duplication (0 in 400-1,000 chromosomes), which suggests to that
duplications are very efficiently eliminated when not under selective
pressure (If we assume that duplications occur just as often in Africa as
in Europe).
All this would favor the notion that, in the classical scheme, after
duplication, both genes must remain functional (either in the old or the
new role) pretty much continuously. There does not seem to be much room
for an "idle" copy that can change any which way until it stumbles onto a
new function.
Unless I am missing something, of course.
Gustavo Maroni
