Lukaszewski, A.J., Kopecký, D., Linc, G.
CHROMOSOMA
121:
201-208,
2012
Klíčová slova:
Abstrakt:
In many species, including wheat, crossing over
is distal, and the proximal regions of chromosome arms
contribute little to genetic maps. This was thought to be a
consequence of terminal initiation of synapsis favoring distal
crossing over. However, in an inverted rye chromosome
arm, the pattern of metaphase I chiasmata was also inverted,
suggesting that crossover frequencies were specific to chromosome
segments. Here, wheat chromosome arms 2BS and
4AL, with essentially entire arms inverted in reverse tandem
duplications (rtd), were studied in the MI of meiosis. Inversion–
duplication placed the recombining segments in the
middle of the arms. While the overall pairing frequencies
of the inverted–duplicated arms were considerably reduced
relative to normal arms, chiasmata, if present, were always
located in the same regions as in structurally normal arms,
and relative chiasma frequencies remained the same. The
frequencies of fragment or fragment + bridge configurations
in AI and AII indicated that of the two tandemly arranged
copies of segments in rtds, the more distal inverted segments
were more likely to cross over than the segments in their
original orientations. These observations show that also in
wheat, relative crossover frequencies along chromosome
arms are predetermined and independent of the segment
location. The segments normally not licensed to cross over
do not do so even when placed in seemingly most favorable
positions for it.
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