[SunilNagpal]

Mathematics/ Probability suggests that any of the possible outcomes can happen at a given event with varied degree of chances (so one should not assume/ expect all those possible outcomes to take place). Any one outcome may happen all the time (on tossing a coin, you have 50% Probability for each outcome on each toss, so as a matter of fact you can keep getting heads all the time or tails all the time as well).

Similarly in the given case, each birth is an isolated event. Whereas there are many outcomes possible, it is very much possible that only carrier females or only affected males keep taking birth)...