Japanese map of the earwax gene frequency: a nationwide collaborative study by Super Science High School Consortium.

Wet/dry types of earwax are determined by the c.538G>A single-nucleotide polymorphism (SNP) in the ABCC11 gene; GA and GG genotypes give the wet type and AA the dry type. The Japanese population may have a dual structure comprising descendants of mixtures between the ancient 'Jomon' and 'Yayoi' populations. We hypothesized that the dry type was introduced by the Yayoi people to the Jomon population where the wet type was predominant, and as the mixture of the two populations has not yet been complete, the allele-A frequency (f(A)) would even now be higher along a putative Yayoi man's peopling route within Japanese islands. To know the frequency, a nationwide Super Science High School (SSH) Consortium collected 1963 fingernail samples of pupils/students from at least one high school/university in every prefecture. All further procedures, DNA extraction, SNP genotyping and gene frequency estimation, were carried out by trained SSH pupils. Although the allele-A frequency varied among the 47 prefectures, the Gifu/Kyoto and Okinawa prefectures showed the highest and lowest values, respectively. Areas with high frequencies included Northeastern Kyushu, Northern Shikoku and Kinki districts, showing a belt-like zone, whereas those with low frequencies other than Okinawa were the Southwestern Kyushu, Hiroshima prefecture and Tohoku districts. The f(A) value in Kinki district was statistically higher than those in prefectures westward and east-northward from it. The result may provide another line of evidence supporting a possible route of the Yayoi-man's peopling in Japan.