Tyrosine aminotransferase and chymotrypsinogen B are linked to haptoglobin on human chromosome 16q: Comparison of genetic and physical distances

Abstract The loci for haptoglobin (HP) and tyrosine aminotransferase (TAT) are known to reside at 16q22. Chymotrypsinogen B (CRRB), which is syntenic with TAT and HP on mouse chromosome 8, has also been assigned to human chromosome 16 but has not been mapped regionally. A linkage analysis was carried out in 13 informative families using RFLPs for these three markers. For CTRB, two Taq I RFLPs with a polymorphism information content of 0.60 derived from haplotype frequencies are described. The most likely order of loci, deduced from triple informative crosses, and their map distances, obtained by pairwise linkage analysis, are HP-7 cM-TAT-9 cM-CTRB. By pulsed-field gel electrophoresis, a physical map covering more than 2000 kb was constructed. A maximum physical distance of about 700 kb was obtained for HP and TAT, which contrasts with the genetic distance of 7 cM (approximate confidence limits 2–18 cM). CTRB is at least 800 kb away from these two markers.