Cytological examination of D. kikkawai and D, leontia from different geographic origins shows quantitative variation of constitutive heterochromatin in the 4th (microchromosome) and Y chromosomes. Four new types of the 4th chromosome and two of the Y chromosome have been discovered in D, kikkawai. When combined with the previous records, a total of 9 types of 4th chromosome and 4 types of Y chromosome have been encountered in natural populations of D, kikkawai. This makes it the most variable

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... metaphase karyotype in the genus Drosophila. In contrcst, its sibling species, D. leontia, exhibits a uniform mitotic karyotype similar to D, bocki. Furthermore, D, kikkawai is highly variable in metaphase heterochromatin in the oriental region, especially in Southeast Asia, which probably represents the center of its distribution, while populations toward the eastern and western bounds tend to be monomorphic which reflect the periphery of the species range. 208 V. BAIMAI, A. TRAIPAKVASIN and 0. KITAGAWA