The allele responsible for sickle-cell anaemia first appeared in the tropical and subtropical regions of Asia, the Middle
East and Africa. It entered the United States of America when individuals were forcibly brought over from Africa. In micro-
evolutionary terms this is an example of
A man who is heterozygous for the disease haemophilia marries a woman who is double recessive for haemophilia. What percentage of their offspring would have the disease?
