Which of these is not a Mendelian disorder?

It is said, that the harmful alleles get eliminated from population over a period of time, yet sickle cell anaemia is persisting in human population. Why ?

A man known to be victim of haemophilia marries a normal woman whose father was known to be a bleeder. Then it is expected that

Pedigree analysis is very important in human beings because

Select the correct match.