Genetic Study on the Local Populations in Mie Prefecture

Abstract

The population structure in Kamishima was investigated. Data concerning the demographic structure and marriage pattern of the islanders are presented and discussed from a viewpoint of population genetics.The results so far obtained are as follows;1. The Kamishima population has been nearly isolated geographically from the neiboring populations for a long time.2. While the population size was estimated to be 500 to 600 during some hundreds years prior to the Mei ji era, it increased in number slowly since the Mei ji era until 1960. After 1960, it has been decreasing much slowly until now, and about 1000 persons are living in Kamishima.3. The mean age at marriage is 26 to 27 years for men and 20 to 22 years for women and it has been raised gradually. From these values we can take about 30 years for the average length of a generation.4. The endogamy rate is calculated to be 91.6%, falling in one of the highest value for isolated populations in Japan reported so far. From this it can be said that Kamishima population has been highly isolated genetically for a long time. This is consistent with the above finding (1.).5. Although the frequency of the first cousin marriages is low, there seems to be many remote consanguinious marriages other than the first cousin, for example, those of second cousin, second cousin once removed, third cousin and so on and those with multifold consanguinity.6. The frequencies of four subgroups of cousin marriages seems to be random.7. The tendency to assortative matings with respect to surnames or relatives is not recognizable.8. The mean inbreeding coefficient is calculated to be 0.02182 to 0.05778 on the basis of the rate of isonymous marriages, which is equivalent to something between the offspring from the first cousin (F=1/16) and the second cousin (F=1/64) marriages.9. Since the greater portion of the inbreeding coefficient is attributed to the random component, random genetic drift has presumably much influenced the genetic structure of Kamishima population.10. These results are consistent with those in our previous report on the distribution of some biochemical genetic markers in Kamishima (TOYOMASU et al., 1977).