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Hultén, Maj A. (2011)
Publisher: BioMed Central Ltd.
Journal: Molecular Cytogenetics
Languages: English
Types: Article
Subjects: QH426-470, Genetics, QH426, Hypothesis
Background: It is now nearly a century since it was first discovered that crossovers between homologous parental\ud chromosomes, originating at the Prophase stage of Meiosis I, are not randomly placed. In fact, the number and\ud distribution of crossovers are strictly regulated with crossovers/chiasmata formed in optimal positions along the\ud length of individual chromosomes, facilitating regular chromosome segregation at the first meiotic division. In spite\ud of much research addressing this question, the underlying mechanism(s) for the phenomenon called crossover/\ud chiasma interference is/are still unknown; and this constitutes an outstanding biological enigma.\ud Results: The Chromosome Oscillatory Movement (COM) model for crossover/chiasma interference implies that,\ud during Prophase of Meiosis I, oscillatory movements of the telomeres (attached to the nuclear membrane) and the\ud kinetochores (within the centromeres) create waves along the length of chromosome pairs (bivalents) so that\ud crossing-over and chiasma formation is facilitated by the proximity of parental homologs induced at the nodal\ud regions of the waves thus created. This model adequately explains the salient features of crossover/chiasma\ud interference, where (1) there is normally at least one crossover/chiasma per bivalent, (2) the number is correlated\ud to bivalent length, (3) the positions are dependent on the number per bivalent, (4) interference distances are on\ud average longer over the centromere than along chromosome arms, and (5) there are significant changes in carriers\ud of structural chromosome rearrangements.\ud Conclusions: The crossover/chiasma frequency distribution in humans and mice with normal karyotypes as well as\ud in carriers of structural chromosome rearrangements are those expected on the COM model. Further studies are\ud underway to analyze mechanical/mathematical aspects of this model for the origin of crossover/chiasma\ud interference, using string replicas of the homologous chromosomes at the Prophase stage of Meiosis I. The\ud parameters to vary in this type of experiment will include: (1) the mitotic karyotype, i.e. ranked length and\ud centromere index of the chromosomes involved, (2) the specific bivalent/multivalent length and flexibility,\ud dependent on the way this structure is positioned within the nucleus and the size of the respective meiocyte\ud nuclei, (3) the frequency characteristics of the oscillatory movements at respectively the telomeres and the\ud kinetochores.

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