Maternal effect as a cause of the difference between the reciprocal crosses in Drosophila pseudoobscura

Reciprocal crosses not infrequently produce different results; this fact is sometimes quoted as an evidence for cytoplasmatic inheritance, although the fallacy of the argument has been repeatedly pointed out. It is to be granted, however, that the cause of the difference between reciprocal crosses has not been adequately analyzed in most cases. An approximation toward such an analysis is now possible in the hybrids between race A and race B of Drosophila pseudoobscura Frolowa.