  Weber (2005) and Rosenberg (2006) independently claim that DNA contains a genetic program that is executed in development, but both deny that this idea depends on the notion that DNA contains semantic or intentional information. They illustrate this point by reviewing the current explanation of the first stages of anterior-posterior pattern formation in Drosophila embryos. This explanation accounts for how a single-celled embryo with an intracellular gradient of bicoid protein (the concentration of bicoid decreases from the anterior to posterior end) develops into a multicellular embryo with 14 parasegments (the first three parasegments later form the head, the next three will form the thorax, and the remaining segments will form abdominal segments). Weber begins by explaining that the bicoid gradient is "generated by the synthesis of protein from an mRNA species that is derived from the mother (by transcription of maternal genes) and is deposited in the egg cell at the anterior end by maternal nurse cells." (Weber 2005, p. 244). He continues by explaining how the biocoid protein differentially activates a set of six gap genes, which in turn differentially activate and deactive eight pair-rule genes, which differentially activate and deactivate segment polarity genes and homeotic selector genes.