Genome-wide characteristics of copy number variation in Polish Holstein and Polish Red cattle using SNP genotyping assay.

Copy number variation (CNV), which results from deletions or amplifications of large fragments of genomic DNA, is widespread in mammalian genomes and apart from its potential pathogenic effect it is considered as a source of natural genetic diversity. In cattle populations, this kind of genetic variability remains still insufficiently elucidated and studies focusing on the detection of new structural genomic variants in different cattle populations may contribute to a better understanding of cattle breeds' diversity and genetic basis of production traits. In this study, by using BovineSNP50 assay and cnvPartition algorithm we identified CNVs in two different cattle breeds: Holstein (859 animals) and Polish Red (301). In Holstein cattle we found 648 CNVs which could be reduced to 91 non-redundant variable genomic regions (CNVRs) covering in total 168.6 Mb of the genomic sequence. In Polish Red cattle we detected 62 CNVs, localized in 37 variable regions encompassing 22.3 Mb of the sequence, corresponding to 0.89 % of the autosomal genome. Within the regions we identified 1,192 unique RefSeq genes which are engaged in a variety of biological processes. High concordance of the regions' distribution was found between the studied breeds, however copy number variants seemed to be more common in Holstein cattle. About 26 % of the regions described in this study could be classified as newly identified. The results of this study will broaden the knowledge of CNVs in genomes of cattle of different breeds and will provide foundations for further research aiming to identify a relationship between this type of genetic variation and phenotypic traits.