I am working on review of mtDNA control region study in human populations.I have come across an issue related to mtDNA genetic diversity so please provide me expert advice on this.
What do you mean by "genetic diversity"? If it is the probability that two random sequences from the population are different, then it cannot be less than zero. And due to great mtDNA genetic diversity, you can find it low in small isolated populations where all individuals are descendants of one grand-grand-mother (hardly probable situation). I guess that the lowest diversiy can be found in Arctic populations (Eskimos, Chukchi, etc).
I agree. The genetic diversity cannot be negative. Thiough Arlequin sometimes shows negative Fst (inter-population diversity) but this is a calculation artefact. But I suppose that you mean intrapopulation diversity, as also Maria suggested. As far as I remember, one very isolated Thailand population (yellow leaves) has ZERO diversity (all population members carry the same mtDNA variant). Try to search this in PubMed.