Distribution of the fushi tarazu (ftz) and even-skipped (eve) gene products in early Drosophila embryos. (a) The ftz gene product can be detected in seven bands around the circumference of the embryo. These alternate with bands where the eve gene is expressed. (b) In a cross-sectional autoradiograph, the ftz bands appear as dark spots (generated by a radioactive label) and demarcate the anterior margins of the segments that will appear in the late embryo.