Linkage disequilibrium and evolutionary relationships of DNA variants (restriction enzyme fragment length polymorphisms) at the serum albumin locus.

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Abstract
Four additional DNA variants (restriction enzyme fragment length polymorphisms) making a total of 8 polymorphic sites at the human albumin locus have been identified. These eight sites were found after screening 689 of 20,000 nucleotides by using c[complementary]DNA probes for albumin with 27 different restriction enzymes. One in 85 nucleotides was therefore potentially polymorphic. The average nucleotide diversity between any 2 randomly chosen chromosomes was calculated to be 1/500. Marked linkage disequilibrium was observed between the 8 variants. Only 7 haplotypes among 256 possible combinations were observed in 160 chromosomes from Caucasoids, Blacks and Asians. Two haplotypes were found in all 3 human races, indicating that their origin predated human racial divergence. The 3 rarest haplotypes appear to represent recombinational events between the more common haplotypes. All crossovers occurred in the same general region. Studies of several nonhuman primates [Pan paniscus, P. troglodytes, Gorilla gorilla, Papio cynocephalus, Pongo pygmaeus] indicated that the origin of 1 haplotype predated the human-African ape divergence. Although it is not possible to rule out maintenance of this tight linkage by selection or fixation, the limited number of haplotypes at the chromosomal site of the albumin gene near the centromere of chromosome 4 may be the result of decreased recombination.