Ultrastructure of the kinetochore inGraphosoma italicum (Hemiptera: Heteroptera)

Ultrastructural analysis of the centromere in the germ-line ofGraphosoma italicum (Hemiptera: Heteroptera) (2n=12 + XY♂) revealed differences between mitotic and meiotic chromosomes. In mitotic spermatogonial divisions a trilaminar kinetochore plate extending almost the entire length of the chromosomes is present. Meiotic chromosomes, on the contrary, lack trilamellar kinetochore plate, although one chromosome end exhibits a round structure which is denser than the remainder chromatin and resembles a “ball and cup” kinetochore. These structures are orientated towards the poles and sometimes show associated microtubules. Additionally, the meiotic chromosomes are surrounded by a complex system of membranes. The possible role of the round structure and of the complex membrane system in meiotic segregation is discussed.