Vol. 37 No. 2, 1998
Heterochromatin Accumulation and Karyotypic Evolution in Some
Biology, Faculty of Science, Mahidol University, Rama VI Road, Bangkok
Baimai (1998) Evolutionary divergence among eukaryotes always
involves genetic changes at different levels of the genome. At the
chromosomal level, heterochromatin differentiation resulting in
karyotypic evolution provides a useful tool for cytotaxonomy of many
groups of animals including the dipteran insects. In our studies,
detectable differences in the amount and distribution of
heterochromatin have been observed in several groups of closely related
species and some sibling species complexes of Drosophila, Anopheles, and Bactrocera, for example, the D. kikkawai complex and the
montium subgroup, the An. dirus
complex and the maculatus group, and the B. dorsalis complex and the Zeugodacus group, respectively.
Most cases, if not all, of our studies point to the fact that inter-
and intraspecific differences in mitotic chromosomes are due to the
acquisition of major block(s) of constitutive heterochromatin in the
sex chromosome(s) and/or autosome(s), particularly at the pericentric
region. Further, quantitative differences in heterochromatin of mitotic
chromosomes can be successfully employed as genetic markers for
separation of cryptic or isomorphic species in these groups of insects.
Although the functional role and implications of heterochromatin in
species differentiation is an unsolved problem, heterochromatin
accumulation in the genome is clearly involved in genetic
differentiation and karyotypic evolution of dipteran insects as
demonstrated in the present study.
Key words: Constitutive
heterochromatin, Mitotic chromosomes, Karyotypic evolution, Dipteran
*Correspondence: Tel: Fax: (662) 6445422, 6448706.