Male-mediated introgression of Bos indicus genes into Argentine and Bolivian Creole cattle breeds

The geographic distribution and frequency of Bos taurus and Bos indicus Y c hromosome haplotypes amongst Argentine and Bolivian Creole cattle breeds we re studied, using cytogenetic and molecular genetic techniques. A complete correspondence between Y chromosome morphology and the haplotype of the Y-l inked microsatellite marker INRA 124 was found in all males examined. The t aurine and indicine haplotypes were detected in 85.7 and 14.3% of the males studied, respectively, although these frequencies varied amongst the diffe rent breeds examined. The geographic distribution of this polymorphism sugg ests a pattern of zebu introgression in South America. The highest frequenc ies of the Zebu Y-chromosome are found in Brazilian populations (43-90%), i n the eastern part of the continent, while it is absent in the southermost breeds from Uruguay and Argentina. Bolivan breeds, at the centre of the con tinent, exhibit intermediate values (17-41%). This east/west and north/sout h gradient of male Zebu introgression could be explained by historical even ts and environmental factors.