Fate of fragments and properties of translocations of holokinetic chromosomes after X-irradiation of mature sperm of Tetranychus urticae Koch (Acari, Tetranychidae).

After irradiation of mature sperm in males of Tetranychus urticae, early cleavage stages were scored for chromosome fragments. As expected from the presumed holokinetic nature of the chromosomes, the majority (94.29%) of the fragments pass mitosis without difficulty. A minority of the fragments is affected by loss (4.76%) or missegregation (0.95%), leading to loss of fragments from cells in a large fraction of fragment-containing eggs after a few divisions. Lethality induced by the irradiation treatment can probably be ascribed to these losses. When meiotic configurations of F1 females are analysed, translocations turn out to be the most frequent type of aberration, often accompanied by recessive lethal mutations, thus adding an extra amount of lethality to the already high number of non-viable haploid offspring of heterozygous F1 females. The frequently occurring infecundity of the F1 females may be caused by mechanical problems in early stages of meiosis (before oviposition), when multivalents are not able to perform the specific turning movements typical for this type of chromosome. According to calculations, univalents in meiotic stages are thought to represent translocated chromosomes rather than independent fragments.