Relationship between crossing-over and chiasma formation in a translocation heterozygote of Atractomorpha bedeli (Acrididae, Orthoptera)

Abstract

A male of Atractomorp/za bedeli (2nd' = 18 + X) was heterozygous for a complex translocation in which exchange involved three non-homologous chromosomes. Unaltered and altered chromosomes constituted special pairs each with proximal homologous segments (interstitial segments) and distal nonhomologous segments. Two of such pairs were" heteromorphic " for unequal length of the distal non-homologous segments. Thus occurrence of a single crossing-over in the proximal segment resulted in equational Al separation for the distal inequality. A good conformity was found between formation of a chiasma in the proximal segment and equational Al separation for the distal inequality. Thus occurrence of a crossing-over corresponded to formation of a chiasma, supporting the view of the chiasmatype hypothesis.

Metaphase I orientation of Robertsonian trivalents in the water-hyacinth grasshopper, Cornops aquaticum (Acrididae, Orthoptera)

“…Indeed, chiasma frequency and position are usually unchanged in spontaneous centric fusions (Colombo, 1987; López-Fernández et al , 1984; Sannomiya, 1968; Southern, 1967). Concurrently, when studied, more than 36% of metaphase I plates showed linear orientation.…”

“…It must be pointed out that in trivalents, it is always polymorphic , and never polytypic or spontaneous centric fusions that present chiasma redistribution to more distal positions. Indeed, chiasma frequency and position are usually unchanged in spontaneous centric fusions ( Colombo, 1987 ; López-Fernández et al , 1984 ; Sannomiya, 1968 ; Southern, 1967 ). Concurrently, when studied, more than 36% of metaphase I plates showed linear orientation.…”

Population cytology of Leptysma argentina Bruner (Leptysminae, Acrididae)

“…Although several spontaneous translocations have been reported in this group only three were complex ones: one in Keyacris scurra where an individual was heterozygous for a translocation involving breaks in four different chromosomes (White, 1963); one in an individual of Chorthippus longicornis heterozygous for two translocations (Coleman, 1947); and one in an individual of A tractomorpha bedeli, heterozygous for a complex translocation involving three non-homologous autosomes (Sannomiya, 1978). According to White (1973) such complex rearrangements would lead to complete sterility and so it is improbable that they could have been inherited from a previous generation.…”