Below is a probability table for ASP(Affected Sib-Pair) with IBD(Identity By Descent), which is one of the major nonparametric methods for complex diseases. Disease allele is full recessive to a wild type allele, which is the only alternative allele in the population, and with full penetrance.

Create the table when the disease allele is (fully) dominant. Allelic association (to some diseases or traits) can almost always observed for human population. Why is it so?
(within 7 lines) What is the common method used to avoid this false signal?
(more than 3 lines and less than 7 lines)