It has recently been suggested from several laboratories that complex synaptic configurations (required for homologous synapsis in the presence of heterozygosity for chromosome rearrangements, or resulting from multivalent formation in polyploids, or even resulting from interlocking of normal bivalents) may be formed at early pachytene, but are altered at later pachytene by dissolution of the central element of the synaptonemal complex, followed by its reinstatement in such a way that only free bivalents, typical of normal sequence homozygotes in diploids, are usually found at late pachytene. It has been suggested that the synaptic adjustment inferred may be a process of widespread occurrence (Moses, M. J. et al., J. Cell Biol. 79:123a, 1978; Rasmussen, S. W. and P. B. Holm, Carlsberg Res. Comm. 44:101-125, 1979). Maize microsporocytes heterozygous for a paracentric inversion in the long arm of chromosome 1 (inversion 4305-25) were studied in this laboratory (in acetocarmine squashes) at early and late pachytene and also at early diplotene. Clear remnants of loop configurations typical of homologous synapsis of the inverted region were found in a number of cells at early diplotene, and synaptic failure of the inverted region was common at both early and late pachytene. In maize microsporocytes a synaptic adjustment process comparable to that which has been reported in mammals seems to be absent.
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