Nucleotide sequence of an RT-PCR amplified portion of FXI exon 11 from platelet RNA. RT-PCR and DNA sequencing were performed as described in the Materials and Methods section using platelet RNA from an individual known to be heterozygous for a T to C polymorphism within amino acid codon 379 of FXI (nucleotide position 1234 of the human cDNA sequence18) and a person homozygous for the wild-type (T) allele. The arrow indicates the position of the polymorphism. Note the signal for both a T and C residue at this position for the heterozygous individual.