Cattle rob(1;29) originating from complex chromosome rearrangements as revealed by both banding and FISH-mapping techniques

Sixteen carriers of rob(1;29) (one of which was homozygous) from six different breeds (four Italian and two Portuguese), two heterozygous carriers of rob(26;29), three river buffaloes and two sheep were cytogenetically investigated in this study by using banding and FISH-mapping techniques (the latter only in cattle and river buffalo). Single- and dual- colour FISH were used with bovine probes containing both INRA143 (mapping proximally to BTA29) and bovine satellite (SAT) DNA SAT I, SAT III and SAT IV (mapping at the centromeric regions of cattle chromosomes). The combined use of these probes, the comparison of rob(1;29) with the dicentric rob(26;29) and with both river buffalo and sheep chromosomes (biarmed pairs) allowed us to hypothezise that rob(1;29) originated from complex chromosomal rearrangements through at least three sequential events: (a) centric fusion with the formation of a dicentric chromosome; (b) formation of a monocentric chromosome with loss of SAT I from both BTA1 and BTA29, most of SAT IV from BTA29 and, probably, some repeats of SAT III from BTA1; (c) double pericentric inversion or, more probably, a chromosome transposition of a small chromosome segment containing INRA143 from proximal p-arms to proximal q-arm of the translocated chromosome.