The egg came first, of course! Anterior-posterior pattern formation in Drosophila embryogenesis and oogenesis.

The anterior-posterior body pattern of the Drosophila embryo is initiated through the action of maternal gene products. In particular, three groups of maternally acting genes (the anterior, posterior and terminal groups) have been shown to direct the synthesis and spatial restriction of the three major organizing activities in the egg. The initial spatial localizations of the maternal organizing activities are established during oogenesis. After fertilization these activities regulate zygotic gene activity along the anterior-posterior axis of the egg.