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| Modern Genetic Analysis Chapter 16. The Genetic Basis of Development Forming Complex Pattern: Establishing Positional Information Genetics In Process 16-4: Studying the BCD gradient The concentration of BCD protein affects AP cell fates. The amount of BCD protein can be changed by varying the number of copies of the bcd+ gene in the mother. Embryos derived from mothers carrying from one to four copies of bcd+ have increasing amounts of BCD protein. (Two copies is the normal diploid gene dose.) Cells that invaginate to form the cephalic furrow (cf) are determined by a specific concentration of BCD protein. In the progression from one maternal copy to four copies of bcd+, this specific concentration is present more and more posteriorly in the embryo. Thus, the position of the cephalic furrow (marked dorsally by the triangle) arises farther toward the posterior according to bcd+ gene dosage. (Adapted from W. Driever and C. Nüsslein-Volhard, Cell 54, 1988, 100.)

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