ddF analysis of exon 11 in a group of normal volunteers. ddF was performed as described in Materials and Methods. The asterisk indicates samples in which the presence of the neutral T to C change at nucleotide 1234 was identified by the appearance of new or shifted bands on the autoradiograph (indicated by the arrows). The sample indicated by the double asterisk comes from a person who is homozygous for the polymorphism, whereas the samples indicated by the single asterisk are from heterozygotes.