The association of centromeres of nonhomologous chromosomes at meiotic prophase in Beta vulgaris L.

Abstract

Centromere association involving two or three nonhomologous bivalents at meiotic prophase of Beta vulgaris and monosomic additions of B. vulgaris × B. procumbens are described. The associations, most conspicuous at late pachytene and persisting until diakinesis, occur abundantly in a small group of genetically related plants. The presence of normal bivalents at metaphase I and the absence of irregularities at later stages show that centromere associations do not disturb meiotic recombination and transmission. A mathematical model proposed to test for randomness with respect to the number of bivalents involved in centromere associations, showed significant difference between observed and expected frequencies. On the basis of our own observations and data from the literature, it is suggested that the associations at pachytene and diplotene are delayed separations of centromere aggregates that arise at premeiotic interphase or during the formation of the synizetic knot. A possible molecular mechanism is discussed.Key words: centromere association, meiotic prophase, pachytene chromosomes, nonhomologous association, sugar beet, Beta vulgaris.