Mapping fragile-sites in the standard karyotype of River Buffalo (Bubalus bubalis, 2n=50)

A fragile-site map has been preliminarily established in the standard karyotype of river buffalo (Bubalus bubalis, 2n=50) with the aim of unmasking 'weak' chromosomal regions in the karyotype of the species. The majority of the breakages took place in the RBA/RBG-negative bands or at the band-interband regions. The most fragile chromosomes were identified as the inactive X, chromosomes 9 and 8, and the active X, with 42, 32, 31 and 30 breakages, respectively. The 400 breakages were distributed in 106 break-sites (BS), with an average intensity of 4 breaks per chromosomal site; (b) the most fragile bands of the river buffalo karyotype were identified as 9q213 with 24 breaks, band 19q21 with 16; inacXq24 with 15; bands 15q23 and 17q21 with 13; band 13q23 with 12, and so on. Preliminary gene mapping analysis revealed that the closest loci to these fragile sites contain genes such as RASA1 and CAST (9q214), NPR3 and C9 (19q19), OarCP09 (15q24), PLP and BTK (Xq24-q25) and EDNRB (13q22), whose mutations are responsible for severe phenotypic malformations and immunodeficiency in humans and mice, and meat quality in pigs. Further cytogenetic and molecular studies are needed to fully exploit the biological significance of the fragile sites in the karyotypes of domestic animals and their relationships with productive and reproductive efficiency.