(A) PCR-RFLP analysis of the Val34Leu polymorphism in exon II of the factor XIII A subunit gene. The fragment amplified from exon II was digested with Dde I. This fragment is 192 bp in length and does not normally contain a Dde I site in either allele. The Dde I site was selectively introduced into the Leu34 allele by the use of a modified primer (see Materials and Methods). Lane 1, molecular size markers; lane 2, DNA from a Val34 homozygote; lane 3, DNA from a Val34/Leu34 heterozygote; lane 4, DNA from a Leu34 homozygote. The expected sizes of the DNA fragments after digestion are shown on the right and schematically at the bottom of the figure. (B) Direct sequencing of amplified exon II from individuals with each genotype. The Val34 and Leu34 sequences are given on the right. The substituted nucleotide G to T causing the Val34Leu substitution is shown in bold type and the position of the base substitution is marked (*).