CHIASMA STUDIES IN STRUCTURAL HYBRIDS. X. FURTHER STUDIES IN <i>ACRIDA LATA</i>

Abstract

A pair or pairs of heteromorphic chromosomes are of special importance for cytogenetic analysis, for reductional and equational separations for the inequality are distinguished at AT. Based on the chiasmatype hypothesis, frequencies of these two types of AT separation are governed by crossing-over in the region of the chromosomes concerned (cf. Mather 1935, Darlington 1937. Observations of frequencies of chiasmata and the types of AI separation in heteromorphic chromosome pairs of various sources have shown close relationship between crossing-over and chiasma formation, supporting the view of the chiasmatype hypothesis (Brown and Zohary 1955, Jamn and Basak 1963, Kayano 1960a, b, Kayano and Nakamura 1960, Noda 1960, 1967, Zen 1961).Nur's (1961) data also support the above view. The present state of the problem has been reviewed by Brown and Zohary (l. c.) and by Whitehouse (1965). The purpose of the present paper is to show additional evidence of a close relationship between crossing-over and chiasma formation, and also to show no reduction of number of chiasmata from diplotene to MI, use being made of structural heterozygotes of Acrida lata Motschulsky (Orthoptera, Acrididae). MATERIALS AND METHODSThree males of Acrida lata Motschulsky were used : (1) A translocation heterozygote, 2n-22 I X, caught at Goshi, Kumamoto Prefecture in 1963, (2) an individual, 2n=22 } X 1B, with a heteromorphic bivalent in primary spermatocytes, which was caught on the campus of Ooita University in 1962, and (3) a heterozygote for a centric fusion, 2n=21 H -X, caught on the campus of Kumamoto University in 1961. The testes were fixed in the mixture recommended by Newcomer (1953) and the preparations of spermatocytes were made employing the usual iron-acetocarmine squash method. RESULTS AND DISCUSSIONCrossing-over and chiasma formation. In the translocation heterozygote the complex of 4 chromosomes was found to pair in 1 (6.5 °o), 1 --1 (91.7 %), 2 a (0.9 %), and 1 A } 2 1 (0.9 %), 217 primary spermatocytes at MI being observed (Fig. 2). Analysis of the configurations of the multiples indicated that a segmental interchange occurred between chromosomes 3 and 9, giving rise to chromosome 39 and 93 (Figs. 1, 2, and 6). The 1) Contributions from the Institute of Biology, Ooita University, No. 72.

Interference relationships in grasshopper reciprocal translocation heterozygotes

“…In this case, the breakpoint seemed to act as a barrier for interference, the different translocation arms being independent from one another. Under the assumption of Sybenga's model, a number of factors could account for such a behaviour; first of all failure of pairing around the breakpoint might be less severe in this translocation, secondly the chromosome arms may be long enough to show a compensatory effect of chiasma formation in normally paired regions far apart from the breakpoint similar to that described by Grell (1962) Sybenga (1975) for a translocation in Acrida lata (Sannomiya, 1968). In both cases a short interstitial region never pairs so that it leaves the translocated segments free to move around until they have completed their pairing.…”

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

“…John and Lewis, 1965;Whitehouse, 1973). Further evidence for the chiasmatype hypothesis has been presented by Noda (1967Noda ( , 1974111 Scilla scilloides, Watanabe and Noda (1974) in Allium thunbergii, and Sannomiya (1968) in Acrida lata.…”

Chromosome polymorphisms and chiasma frequency in two populations of Staurorhectus longicornis (Orthoptera-Acrididae).

“…There are many studies dealing with the influence of different chromsome rear rangements on chiasma formation in several species of Orthoptera (Hewitt and John 1965, John and Hewitt 1966, Sannomiya 1968, Shaw 1971a, Hewitt 1979. Saez (1956) and Mesa (1956) have described the haploid number of Staurorhec tus longicornis (G. Tos) studying only a few individuals.…”