Robertsonian fusion and centric fission are unique in being readily identified in comparative karyotype studies since both result in concomitant changes in chromosome morphology and chromosome number.
Centric fission is the consequence of a break within the centromere of a single metacentric producing initially two structural telocentrics whose raw ends have the capacity to fuse after replication.
Alteration by centric fission of the diploid number in Vicia faba L.
grammicus complex, they should still be negatively heterotic." Meiotic disruption has not been demonstrated in hybrid individuals heterozygous for the centric fission mutations that delineate most S.
1992c), the F5 and FM2 cytotypes differ by centric fissions at chromosomes 1, 3, and 6 ([ILLUSTRATION FOR FIGURE 2 OMITTED] in Sites et al.
1995), but this study provides no direct evidence for underdominance in the Tulancingo hybrid zone associated with the centric fissions of chromosomes 1, 3, 4, and 6 or the pericentric inversion of chromosome 4.
Hall (1973) attributed the morphology of chromosome 2 in the FM2 cytotype to a single centric fission of the ancestral bi-armed chromosome 2.
Formation of the [AR.sub.c] trivalent [ILLUSTRATION FOR FIGURE 4D OMITTED] was essentially identical to that observed for other centric fission trivalents in this species (Reed et al.
Meiotic data from [R.sub.c] recombinants suggest that the centric fission of chromosome 2 poses no meiotic problems when in combination with the F5 chromosomal complement ([AR.sub.c]) but may lead to increased an-euploidy in combination with FM2 ([B.sub.d][R.sub.c]).