A geneticist is examining culture of fruit flies and discovers the single female with strange spots on her legs. The new mutation is named as melanotic. When female melanotic fly is crossed with the normal male, the following progeny are manufactured: 123 normal females, 125 melanotic females, and 124 normal males. In following crosses with normal males, melanotic females are often obtained, but never any melanotic males. Give a possible explanation for inheritance of melanotic mutation. (Hint: The cross generates twice as many female progeny as male progeny.)