The investigation examined the relationship of genetic structures and the relations of Hmong, Karen and Iu Mien as well as genetic variations due to migration after marriage and genealogical relationships among the ethnic groups by using the X chromosome, Y-linked microsatellite markers and mitochondrial DNA from white blood cells as the research instruments. Furthermore, 14 positions of microsatellite genotype in the X chromosome, 15 positions of microsatellite in the Y chromosome, and base order of the mitochondrial DNA in the hypervariable segment 1 area in the control region were analyzed. DNA quantities were increased by the polymeres chain reaction.
    
It is found that genetic variations were due to the diversity of subgroups or individuals. Migration after marriage also affected the genetic structures of the ethnic groups. The subgroups of each tribe are closely related genealogically, except the Iu Mien from three provinces, whose genetic structures are different probably due to different migration routes and times of migration. It is further found that the subgroups of each tribe are genetically closely related and it is possible that they might have had the same ancestors.
    
The genetic structures of the three ethnic groups are found to be different with a low percentage of variation, indicating that the ethnic groups are genetically closely related. This may be due to the fact that the origin of Karen ancestors was in the Yellow River region in China and there was a genetic mixture of southern Chinese who were the ancestors of both Hmong and Iu Mien before their southward migration.             
     
1. Differences of migration after marriage affected the genetic structures of the ethnic groups. The variation of the Y chromosome of the Karen, where the groom moves in with the bride's family, is more varied than that of the Hmong. Conversely, the variation of mitochondrial DNA of the Hmong, where the bride moves in with the groom's family, is more pronounced than that of the Karen.
    
2. Due to the adoption practices of the Iu Mien, the variation of the Y chromosome is more pronounced than that of the Hmong and the Karen.
    
3. Migration rates calculated from the genetic variations of X and Y chromosomes and mitochondrial DNA indicate that men migrated more than women in the group where the groom moves in with the bride's family after marriage (Karen), and women migrated more than men in the groups where the bride moves in with the groom's family after marriage (Hmong and Iu Mien).