This article is from the Asthma FAQ, by Patricia Wrean and Marie Goldenberg email@example.com with numerous contributions by others.
No, asthma itself is not hereditary, but there does seem to be
a hereditary component to the tendency to develop asthma. In
_All About Asthma_, Dr. Paul states that if neither parent has
asthma, the chances of each of their children having asthma are
less than 10%. When one parent has asthma, the chances rise to
25%, and when both parents have asthma, the chances climb to 50%.
(Actually, there is considerable disagreement among my sources
as to the exact numbers, but all agree that the chances climb
dramatically if one or both parents have asthma.)
Similarly, if one or both parents have allergies, the chances
of each of their children having allergies are 35% and 65%,
respectively, compared to a less than 10% chance if neither
parent has allergies.
However, Dr. Paul cautions that "children don't inherit asthma
itself, but the tendency to develop it." Whether or not an
individual develops asthma is also influenced by their exposure
to various other factors such as infections, irritants, and