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Loss of complementation and the logic of two-step meiosis M. ARCHETTI

Summary: Loss of complementation and the logic of two-step meiosis
De´partement de Biologie, Section Ecologie et Evolution, Universite´ de Fribourg, Fribourg, Switzerland
The two problems of two-steps meiosis
The function of a normal meiosis is to produce haploid
gametes, that is, to halve the genome size before mating.
However meiosis begins with a duplication of chromo-
somes, which is followed by two divisions. Why is
meiosis such a two-step process [2n!4n!2(2n)!4(n)]
instead of a much simpler one-step division [2n!2(n)]?
It is possible that the two steps are just a relict of the
mitosis from which meiosis originated, but there seems to
be no compelling reason why the first duplication cannot
be suppressed. In fact, some diploid protists appear to
produce gametes by one-step meiosis (Raikov, 1982;
Kondrashov, 1997), a single division without prior rep-
lication, producing two daughter cells with haploid sets of
chromosomes. One-step meiosis has been reported for
Pyrsonymphidae (Oxymonadida), Parabasalia (Hyper-
mastigotes), Microsporidia, some Dinoflagellates, and


Source: Archetti, Marco - Department of Organismic and Evolutionary Biology, Harvard University


Collections: Biology and Medicine