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

The loci for haptoglobin (HP) and tyrosine aminotransferase (TAT) are known to reside at 16q22. Chymotrypsinogen B (CTRB), 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 TaqI 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 pair-wise 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.