Very close linkage between HLA-B and Bf inferred from allelic association

THE human leukocyte antigen loci (HLA, previously HL-A) are known to be closely linked to the locus defining factor B of the alternative complement pathway1. The B-factor locus was previously termed GBG (glycine-rich β-glycoprotein) and is now known as Bf. If the consequences of recombination do not impair survival we may use data on allelic association (sometimes termed linkage disequilibrium) as a rough estimate of the upper limit of the recombination fraction, θ. This approach has advantages where linkage is very close and the frequency of laboratory and other errors in ascertaining recombinants is greater than the recombination frequency. By typing two or more members of families we have defined 100 apparently independent haplotypes with the HLA-B allele B8 and all had the Bf allele S. These observations were fairly evenly divided between Iceland, north-west Newfoundland and Labrador, Central England and Norway. Figure 1 shows a ‘family tree’ of these populations.