✦ LIBER ✦

Is crossover between the X and Y a regular feature of meiosis in mouse and man?

✍ Scribed by T. Ashley

Publisher: Springer Netherlands
Year: 1985
Tongue: English
Weight: 515 KB
Volume: 66
Category: Article
ISSN: 0016-6707
DOI: 10.1007/bf00128036

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✦ Synopsis

There has long been an assumption that normal disjunction of the sex chromosomes of all mammals is assured by synapsis of a region of homology between the X and Y and that an 'obligatory' crossover with chiasmata formation follows. Evidence is presented here that much (if not all) observed synapsis between the X and Y in mouse and man is nonhomologous and that crossing over most likely does not occur as a normal event in these organisms. The X and Y have desynapsed to a mere terminal association by the time of pachytene DNA synthesis, generally considered to be associated with crossing over. Recombination nodules or 'bars' observed on the X and Y of human spermatocytes are also present at the wrong substage of pachytene and are insufficient in frequency to account for an'obligatory' crossover between the X and Y and thus assure normal disjunction. Instead it is suggested that orientation and disjunction of the sex chromosomes is mediated in these species by an achiasmatic telomeric association.

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