Pairing of identical chromosomes in an isogenic tetraploid

Abstract

SUMMARYMeiotic pairing is described for a completely homozygous tetraploid derived from successively doubled haploid barley. The high quadrivalent frequency (4.58/cell) in cells with many chiasmata is indicative, either of discrete pairing at only two independent synaptic sites per chromosome or of continuous pairing amongst many sites in close proximity. A high frequency of discordance amongst ring quadrivalents (20.8 per cent) leads to lagging and irregular segregation in at least 20 per cent of first meiotic divisions.

Variation at metaphase-I inLathyrus

“…Univalents accompanied by trivalents out-numbered pairs of univalents in a ratio of 8.67:1 but trivalents were, in turn, much less frequent than quadrivalents (1:8.38). The frequency of quadrivalents did not differ significantly from two-thirds of all tetrasomes (4.36 vs 4.67/PMCs) (t£491 = 1.660, P>0.10), a value based random association of two pairing initiators on each homologous chromosome (CALLOW et al 1984). The 50 PMCs examined exhibited 15 different pairing patterns.…”

Evidence for preferential pairing in telotrisomic plants of rye

“…Deviations from this ratio have been taken as evidence of preferential pairing. However, the existence of several synaptic initiation points per arm would lead to multivalent frequencies higher than 2/3 because partner exchanges might occur more frequently as it has been reported by John and Henderson (1962), Sybenga (1975) and Callow et al (1984). There are some discrepancies concerning the meiotic configurations which should be used for the approach.…”

“…Due to the impossibility of distinguishing specific chromosome arms with such techniques, pairing preferences have been indirectly determined by using theoretical models often based on severe restrictions such as assuming that, 1. all chromosomes of different sets and all chromosomes within the same set have the same probability of pairing. This is reasonable only for very special materials such as isogenic tetraploids newly derived from successively doubled haploids (Callow et a!., 1984).…”

“…Most attempts to study pairing preferences in aneuploids and polyploids have been made from the analysis of meiotic configurations at metaphase I, with conventional staining techniques (John and Henderson, 1962;Timmis and Rees, 1971;Sybenga, 1975;Elçi and Sybenga, 1976;Jackson and Hauber, 1982;Chapman, 1984;Callow et aL, 1984). Due to the impossibility of distinguishing specific chromosome arms with such techniques, pairing preferences have been indirectly determined by using theoretical models often based on severe restrictions such as assuming that, 1. all chromosomes of different sets and all chromosomes within the same set have the same probability of pairing.…”

Developments in the meiotic analysis of hybrids. I. Review of theory and optimization in triploids

“…The results are mixed. The studies of Morrison & Rajhathy (1960) and Callow et al (1984), for example, show independence between chromosome arms, whilst others, e.g. Timmis & Rees (1971), Kuspira et al (1984), , show an excess of bivalents.…”