There is specific term that I can not think of describing the absence of genetic anomalies in an isolated population, due to the fact that in that the recessive traits tend to be incompatible with life. There is another term for the proliferation of non-lethal mutations in an isolated population The prime examples are the difference in incidence of genetic anomalies in the Amish and Mennonite societies, although they come from fairly similar stock, and are both fairly inbred.
Are you talking about founder effect? Population bottlenecking? Or random genetic drift? Granted, I’m not a population geneticist, but I did get a PhD in genetics and I am not familiar with that phenomenon.
There is genetic homogeneity, which is a lack of variation in the gene pool of the population, but this is an effect of isolation (geographical or selective). “Genetic anomaly”, in the general use of the term, typically is an analog to “mutation”, though I don’t think it has a precise usage in technical jargon. Mutation occurs at a roughly constant rate for the same parts of the genome of different members of a species given the same environment.
I’m also not clear regarding your statement that “…recessive traits tend to be incompatible with life.” Recessiveness and dominance with regard to phenotypical expression are relative concepts; while a deliritous trait that would be self-terminating (or rather, lethal to its carrier) could propegate as a recessive trait most recessive or intermediate genes are not harmful, and in fact many impart an advantage; the light skin of the Nordic people, for instance allows for the production of vitamin D. The vast majority of genetic mutations are neutral and occur in the junk DNA which accumulate as harmless–or at least, mostly harmless–inoperative alleles.
The “difference in incidence” (I assume you mean regarding the amount of variation) between Amish and Mennonite populations probably stems somewhat from the smaller and more self-contained Amish populations. The Mennonites, with their acceptance of new-fangled heathenous gadgets like horseless carriages and electrical iceboxes, tend to get out a bit more and at least mingle with a larger portion of their own gene pool, I expect.
Stranger