Cytogenetic characterization, frequency and distribution of rob t(1;29) in some Italian and Portuguese cattle breeds

Since the discovery of rob(1 ;29) (Gustavsson and Rocborn, 1964) and the demonstration of its deleterious effects on fertility (Gustavsson 1969), this translocation has widely been found in all the world, in more than 70 different cattle breeds (Popescu and Pech, 1991), especially in the meat breeds. The number of breeds carrying this translocation is certainly higher than those reported by Popescu and Pech (1991), considering the data published after this study, although the studies on this translocation have drastically been reduced in the last 15 years. One of the reason which can explain this phenomenon is the parallel increasing studies in molecular cytogenetics (gene mapping). However, although various studies have been undertaken to characterize this famous abnormality, its chromosome evolution still remains understood. Indeed, the large block of constitutive heterochromatin (HC) present in this translocation, almost entirely in the proximal q-arms, do not agree with the C-banding patterns of other biarmed chromosomes (sheep, river buffalo), originated by centric fusion translocations and showing very small amounts of HC. This means that cattle rob(1;29) is still evolving by progressive reduction of HC. The lack of HC in p-arms of this translocation suggests a loss of HC (and centromere) from BTA29, as demonstrated by GBA+CBA-banding technique, although the large block oh HC at the proximal q-arms may suggest a retention of HC in this region. The FISH-mapping with D29S16 (INRA143), a marker mapping at the proximal region of BTA29, in a carrier of this translocation revealed the presence of FITC-signal on the proximal q-arm region suggesting a possible pericentric inversion following the centric fusion events (Eggen et al. 1994). Studies we have been doing in different carriers from different breeds by using the same probe (D29S16) confirm this result with some variation in the position of the FICT-signals from the centromere to proximal q-arm region, probably due to the polymorphism of HC. However, FISH-mapping studies on river buffalo chromosome (BBU) 5p (homoeologous to BTA29) with D29S16 revealed clear FITC-signals on the proximal region of BBU5p. This demonstrates that the two biarmed chromosomes (BBU5 and rob1;29 of cattle) followed two different ways during their chromosome evolution, although that of rob(1;29 of cattle is still not ended. A recent study employing molecular markers containing three different type of satellite DNA (SAT I, SAT III and SAT IV) suggested two-step models of dynamic evolution of rob(1;29): a rcp between SAT III of BTA1 and SAT IV of BTA29, followed by the lost of segments containing SAT I of BTA 1 and some SAT III and SAT IV repeats of BTA29. A second step involves the elimination of the SAT I block from intermediate chromosome (Chaves et al. 2003). Data on the frequency and distribution of some Italian and Portuguese cattle breeds is also reported.