Genetic differentiation of blood polymorphic systems among three isolated human populations in central Japan.

An isolate population, which more or less genetically deviates from neighboring populations, sometimes comprises subpopulations with different gene frequency distributions within it. It is not always easy to, however, assess the degree of genetic diversity among subpopulations. Choosing small isolated population, on which biological, demographic, historical, and marital data are relatively easy to accumulate, may have various advantages in solving this problem. There are already some reports on genetic differentiation among small isolated populations, for example, from Amerindian tribes (Neel & Ward, 1970), Italian alpine villages (Cavalli-Sforza, 1969), Bougainville islanders (Friedlaender, 1975), etc.. In Japan, however, relatively undisturbed populations whose mode of life reflects the circumstances under which the genetic diversity has been developed and whose population sizes are still kept considerably large are rapidly decreasing in number. With respect to the local genetic differentiation in Japan, the reports by Nei & Imaizumi (1966abc) are the only series of extensive studies so far made, although these deal with the ABO system alone. During the past five years, we have been engaged in an intensive genetic study of the three villages in Mie Prefecture in central Japan. These are small isolated populations which seem to meet the above qualification. 1 This paper is an attempt to assess the degree of genetic differentiation by the coefficient of gene diversity (Nei, 1973) in the small area where the three populations exist and to specify the factors responsible for their differentiation. A series of studies have already been made on blood polymorphism distribution in Kamishima Island (Toyomasu et al., 1977) and in Toshi-jima Island (Toyomasu & Katayama, 1979), on the demographic and breeding structure in Kamishima Island (Katayama et al., 1978), and on the genetic relations among the three populations (Katayama & Toyomasu, 1979). The information sources of this paper are mostly these. Fig. 1 shows the location of the study populations. (1975). They belong to Toba City of Mie Prefecture and are also adjacent to Aichi Prefecture. These villages have been inhabited since the Kofun period (about the 4-7th c.) and were occupied in 1889 respectively by 860, 2556, and 978 people (Nakaoka ed., 1970). The inhabitants live by fishery in Kamishima and Toshi, and by semi-fishery and 2 semi-agriculture in Momotori. Traditionally there have been few facilities of communication between them except via Toba, and at least during last 100 years only a few intervillage migrations have been recorded even between Toshi …