Frequencies

Hi Alla,
I'm sure you're sick of helping me by now but what do you make of this qn?

-Dunkers are a secluded group originally from rhineland germany before settling in pennsylvania USA during 18th century. Since then they have remained secluded in marriages and customs. The frequency of ABO blood types found in the Dunkers compared to the surrounding American pop and present day rhinelanders is:

Group - no. people tested-Blood frequencies: A......AB......B...........O
Dunkers...228...........................................0.61...0.02....0.04....0.33
Rhinelanders....3036..................................0.45....0.05.....0.10.....0.40
eastern USA...30000.................................0.40.....0.04.....0.12.....0.44

What explaination would you offer to account for the different frequencies amoung Dunkers compared to both the other groups. (you may need to think of some historical facts to help here)

-I'm not entirely sure what kind of answer they are looking for here. Would it be anything to do with the population size and the fact that selection is occuring within the dunkers?
Any ideas are much appreciated!

I am not sure I know what the answer should contain. I would say that Dunkers that moved originally to start this colony was a relatively small group that did not represent original population and, therefore, HW equalibrum does not apply to it (too many violations). The population is still small, so interbreeding (non-random mating) probably affects the blood type occurrence percentages.