An Extreme Karyotype in an Orthopteran Insect

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Abstract
The caryotype of Dichroplus silveiraguidoi is composed of 2 pairs of metacentric, 1 pair of acrocentric, and an unequal pair of X-Y chromosomes. This extraordinary case of an orthopteran with 2n (male)= 8 chromosomes stands out because not only the diploid number, but also the number of chromosome arms or "fundamental number" has become radically altered. The derivation of the Dichroplus caryotype from the ancestral one, must therefore have involved not only centric fusions of the primitive acrocentric but also "loss" of several chromosomes. The probable mechanisms involved in the production of this extreme cytological evolutionary transformation are discussed. Morphology and behavior of the bivalents and XY pair during meiotic divisions is described.

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