Abstract
We used a molecular approach to search for maternally expressed genes in Drosophila melanogaster. The relative merits of differential and competition screens were analyzed in a series of reconstruction experiments using either purified phage plaques or derivative DNA sequences. In the course of this study, we isolated 5 clones whose RNA level varies during early embryogenesis. Three gastrula differential clones, b4, b8 and d3, are present in numerous copies in the genome; clone b4 hybridizes with the copia-like B104 repetitive sequence described by Scherer et al. We also isolated 2 maternally-expressed genes, not previously identified in either classical genetic or similarly molecular-based screens. These clones, b11 and d6, map at cytogenetic positions 98F and 4F respectively, on the polytene chromosome map.