Gentics and linkage relationships of the C3 polymorphism: discovery of C3‐Se linkage and assignment of LES‐C3‐DM‐Se‐PEPD‐Lu synteny to chromosome 19

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Abstract
The C3 complement system was examined in our Danish material of normal families, which had earlier been examined for 59 marker systems, and in a myotonic dystrophy family material. A total of 8 alleles were recognized, with allele frequencies as follows: C3*S = 0.7902, C3*F = 0.2018, C3*S rare (3 lumped together) = 0.0036, C3* F rare (2 lumped together) = 0.0024; a silent allele was recognized in three families and its frequency to C3*QO = 0.002. The distribution of unrelated inviduals did not deviate significantly from the Hardy‐ Weinberg expectation, it was not siginicantly different between the sexes, and the for none of the mating types was there any significant deviation from the expected ratios of children.As to linkage relationships of C3 with market systems and with myotonic dystrophy, there was evidence (most of it first presented at the 6th International Congress of Human Genetics, Jerusalem 1981) for synteny with ABH secretion (Se): C3‐Se (males) ẑ= 4.35, θC = 0.12 and with Lewis secretion (LES): C3‐LES (males ẑ= 3.63, θC = 0.04). There were indicative or suggestive lod scores for Se‐PEPD (males & females ẑ= 2.41, θC = 0.00), C3‐Lu (ẑ= 1.88, θC = 0.15), C3‐DM (ẑ= 1.69, θC = 0.06) and PEPD‐C3 (male ẑ= 0.95, θC = 0.17). The most likely sequence of these 6 systems would appear to be LES‐C3‐DM‐(Se‐PEPD)‐Lu and the synteny would reside on chromosome 19.