Population genetic studies using isoelectric focussing in the Asian, Pacific and Australian area

Abstract

Approximately four thousand blood samples from various ethnic groups in the Asian, Pacific and Australian area have been subjected to isoelectric focussing (IEF) to determine the subtyping of the proteinase inhibitor (PI), transferrin (TF), vitamin D-binding protein (GC) and phosphoglucomutase-1 (PGM1) systems and typing of the thyroxine-binding globulin (TBG) system. Furthermore, the proposed physical association between the PI and TBG proteins has been reexamined. A considerable variation has been observed in the distribution of the PI, TF, GC and PGM1 subtypes and new variants have also been detected at these four loci. The mean heterozygosity per locus detected by IEF varies from 0.40-0.54. This is much higher when compared to the values of 0.13-0.23, obtained by conventional methods of electrophoresis. Some common alleles at each of these four loci show interesting patterns in their distribution. Maximum values of the PI*M2 allele are encountered in Australian Aborigines and Papua New Guinea Highlanders, whereas Asiatic Indians are characterized by having high frequencies of the PI*M3 allele. The TF*C2 allele is present with a relatively high frequency in Asian populations but, in contrast, Australian Aborigines, Micronesians and Melanesians have a low prevalence of this allele. The TF*C3 allele is present at polymorphic 1 evel only in Asiatic Indians. For the GC locus, the highest frequency of GC*1S is found in Asiatic Indians. By comparison, east and southeast Asians are unique in having maximum values of the GC*1F allele. Most of the population groups in the Australian-Pacific area have almost similar values for the frequencies of the GC*1S and GC*1F alleles and these values are intermediate between those observed in Asiatic Indians and in east Asians. At the PGM1 locus the PGM1*1- allele has been detected with a high frequency in Melanesians, Australian Aborigines and Indonesians from the Lesser Sunda Islands, whereas, east Asians and Indian populations IV have approximately half this frequency. Moreover, Indian populations are distinctive in having a higher frequency of the PGM1*2+ allele. However, the lowest values of this allele are recorded in Micronesians. The Polynesians, except for the Cook Islanders, are characterized by having the highest frequency of the PGM1*2- allele. These values are in contrast to the Papua New Guineans and Australian Aborigines where the frequency of the PGM1*2- allele reaches its minimum values. The gene frequency data from the PI, TF, GC and PGM1 loci have been used to calculate Nei's genetic distance and to use the distance values to demonstrate the genetic relationships between the Asian, Pacific and Australian Aboriginal populations studied and then between these populations and Europeans, Black Africans and Black Americans. The genetic distances for each individual locus have been calculated first and then the combined distances obtained from data for the four loci have been computed. The genetic distances obtained from the four loci employing the IEF data are then compared with those obtained using conventional methods of electrophoresis. The data indicate that conventional techniques do not permit adequate discrimination between the populations since the clusters of populations formed are not supported by other types of analyses. For example, Chinese appear to have close affinities with Europeans, and Australian Aborigines are similar to Africans, whilst Asiatic Indians have a close relationship with Fijians and Samoans. However, the use of IEF makes possible discrimination between these populations in accord with accepted views on relationships between peoples in Asia, Europe and Africa. Here Black Africans and Black Americans are at one extreme of the distribution whilst Australian Aborigines and Highlanders in Papua New Guinea are at the other extreme: Europeans and Asiatic Indians are closely related to one another. A separate analysis was made also of the genetic relationships between the north Indian caste groups. It shows that Arora and Rajput cluster together strongly, and that genetically they are closer to V Brahmin than to Vaish or Scheduled Castes. In addition, the tribal population of Soliga, in south India, is distinct from non-tribal populations. However, the non-tribal south Indian series cluster closely with the main caste groups in north India. In the TBG system a genetically determined electrophoretic slow variant, TBG S, which is indistinguishable from the variant found in Black Africans, has been observed with polymorphic frequency in Melanesians and Polynesians. This variant has also been observed sporadically in Micronesians and in the Indonesian series from the Lesser Sunda Islands. However, east Asians, Asiatic Indians and Australian Aborigines were found to be monomorphic for TBG. Reexamination of the proposed association between the PI and TBG proteins indicates that both these proteins are clearly independent and the previously reported association between PI and TBG appears to be an artefact of the method used.