A new look on the role of the diffuse stage in problems of plant and animal meiosis

Especially in plant hybrids and polyploids, the diffuse stage occurring between pachytene and diplotene can be a source of the following meiotic defects: (1) difficulties in stainability or fixability of diplotene or diakinesis chromosomes, (2) desynchronisation of meiotic stages in the anther. (3) timing upset of meiosis, defects in spiralisation, (4) the irregular occurrence of nonhomologous multivalent associations or stickiness in diakinesis or metaphase I, (5) normal anaphase configurations after a strongly aberrant diakinesis stage, (6) irregular occurrence of anaphase 1 bridges of uncertain origin, (7) variable chromosomal behaviour in different cells, anthers and buds in the same plant. The literature on plants where the diffuse stage was reported is reviewed. As similar defects are found in meiosis of many other plants, the diffuse stage is supposed to be widespread in plant meiosis but as it has an interphase‐like structure it is overlooked in squash preparations. The aberrations are believed to be caused by disturbances of the folding process between the diffuse stage and diakinesis, due to a different constitution of chromosomes from different parents or to internal unbalance of chromosome sets in haploids. polyploids and hybrids. Presumably, spontaneous breaks in the chromatin fibers (23 nm) and exchanges sometimes occur during prophase. As the chromatin fibers are the real functional chromatids, the exchanges are regarded as chromatid aberrations.