Fig25-11

Dosage effects on maternal genes in Drosophila

The differentiation of the Head (Cephalic) and Thoracic regions is recognizable early in development by the formation of the cephalic furrow. The position of the furrow is determined by an anterior / posterior gradient of BCD protein in the maternal cytoplasm. A wild-type, diploid fly has two copies of the bcd⁺ gene (2X), which generates a shallow gradient and forms the furrow at the typical position. Increasing the number of bcd⁺ genes (3X or 4X) in the mother increases the amount of BCD protein produced at the anterior end of the larva, which steepens the gradient (darker shading) and moves the furrow more posteriorly. Conversely, a fly with only one bcd⁺ gene (1X) has a shallower gradient, and the furrow moves anteriorly.