Fifteen different restriction fragment length polymorphisms (RFLPs) were detected in the human genome using 19 cloned DNA segments, derived from flow-sorted metaphase chromosomes or total genomic DNA, as hybridization probes. Since these clones were selected at random with respect to their coding potential, their analysis permitted an unbiased estimate of single-copy DNA sequence heterozygosity in the human genome. Since our estimate (h = 0.0037) is an order of magnitude higher than previous estimates derived from protein data, most of the polymorphic variation present in the genome must occur in non-coding sequences. In addition, it was confirmed that enzymes containing the dinucleotide CpG in their recognition sequence detect more polymorphic variation than those that do not contain CpG.

Pregnancy specific beta-1-glycoprotein (PSBG), a major product of the human placenta, is encoded by multiple genes. Southern blot hybridization of human × rodent somatic cell hybrid DNAs with a cDNA specific for one member of the PSBG gene family allowed us to map this gene to human chromosome 19. Further analysis using hybrids with subchromosomal segments of 19q revealed that the gene maps to the distal segment of region 19q 13.1.

Pregnancy-specific beta 1-glycoprotein (PS beta G) is a heterogeneous product of the human syncytiotrophoblast, closely related to the CEA-NCA multigene family. In the present study, immunoscreening was carried out with anti-PS beta G antibodies to isolate cDNA sequences from a placental lambda gt11 expression library. One 1847-bp cDNA clone comprising the major portion of the coding sequence of a putative 48-kd peptide was sequenced and characterized. Hybridization of human genomic DNA to the PS beta G sequence revealed a complex pattern of restriction fragments, a finding well in agreement with the assumption that there are several independent PS beta G genes. A variable PstI band was found in human DNA. Transfer blot analysis of human placental RNA identified transcript of 2.2kb and 1.7kb that appear transiently with increasing levels of expression during gestation. No hybridization of PS beta G cDNA to human RNA from liver, kidney, heart, thyroid, and ovary was observed. In analyses of placental RNA from mouse, goat, sheep, and cow, no corresponding transcripts could be detected, and DNA hybridization under low-stringency hybridization conditions resulted in very faint cross-reacting bands, presumably indicating sequences that were scarcely related. However, PS beta G-specific DNA sequencies with similar restriction patterns were found in primates. These results are compatible with the assumption of late evolutionary development of certain PS beta G sequences.

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