The Evidence for Localized Chiasma Formation
نویسنده
چکیده
ECENT studies of the highly differentiated pachytene chromosomes of R the tomato have indicated that this plant can be used in the analysis of chromosome structure in relation to chromosome behavior and gene location (BROWN 1949; BARTON 1950). In general, the twelve paired chromosomes of the tomato pachytene complement are differentiated into densely staining (chromatic) regions proximally on either side of the centromere, and lightly staining (achromatic) regions distally. Each achromatic region terminates in a well-defined telochromomere. Chromosome 2 is the only member of the complement with one arm which has no achromatic region. This short chromatic arm of chromosome 2 bears the nucleolar organizer. Previous investigators have suggested that few or no chiasmata are formed in this short chromatic arm (LESLFY 1937; BROWN 1949). The present paper presents further evidence that chiasma formation and crossing over occur in the achromatic regions, with little or no incidence in the chromatic regions of the chromosomes of this plant.
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