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Botaniska Notiser 1947, Häfte 59. Lund
Non-random distribution of chromosomes
at meiosis in triploid Allium Schoenoprasum.
By Nils Nybom.
It is generally assumed that, at meiosis in triploid plants, the
extra set ol’ chromosomes is distributed at random to the two poles at
the first division (cf. Darlington, 1937). Oeterminations of the
cliro-mosome numbers al M II or in the pollen grains in triploids of
Hya-cintlius, Tulipa, Petunici, Triticum and Allium have shown that in the
main the distribution of chromosomes is in agreement with a binomial
distribution, generally möre or less displaced to the lef t owing to
chro-mosome elimination through lagging. Concordantly, when studying the
distribution of the chromosomes at meiosis in triploid Lolium perenne,
Myers (1944) found that ->the distribution at anaphase I also was
consistent with llie hypothesis of cliance position of the unorientated
metapliasé I univalents and random assortment of the extra
chromosomes of the trivalenls».
There have, however, also been observed some deviations. Thus,
Satina and Blakeslee (1937) in triploid Datum found an »apparent
tendency for the extra chromosomes to ’go with the crowd’ in
disjunc-tion», which gåve rise to an over-representation of llie extreme
chro-niosome numbers. They did nol find any plausible explanation of this
phenomenon.
Ön llie contrary, an under-representation of the extreme
chromo-some numbers was found by Darlington (1929) in triploid
Tradescan-tiu. In 1944 Darlington and Mather attributed this non-randoniness
lo an »overcrowding at meiosis».
A third case of non-random distribution of interest in this
con-nexion is known from Drosophila. According to Beadle (1935), the X
chromosome trivalent of triploid females of D. melanogaster orients
itself »selectively» in relation to the other trivalents, resulting in an
equalization of the size of the anaphase groups.
Ön the other hand, with the exception of the related Drosophila
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