Heterochromatin variation in chromosome X in a natural population of Anopheles willmori (Diptera: Culicidae) of Thailand.

Among the eight families of Anopheles willmori derived from individual wild-caught females collected from Chiangmai Province (northern Thailand) and examined, four isofemale lines showed variation in the X chromosome, including the normal X1 and three aberrant types (X3, X4 and XL). It is postulated that these different types of X chromosomes could have arisen as a result of spontaneous chromosomal rearrangements involving tandem translocation and paracentric inversion followed by acquisition of constitutive heterochromatin. Such rare events of chromosomal changes have become established in the natural population of An. willmori in northern Thailand.