Molecular cytogenetic screening for chromosomal abnormalities in agricultural species

Chromosome translocations have been shown to reduce fertility in agricultural species leading to reduced pregnancy rates and/or small litter sizes. With an increasing emphasis in modern farming on the use of a small population of males for artificial insemination, the potential economic and environmental costs of using subfertile boars and bulls are significant. An increased need for novel tools to facilitate rapid, cost effective chromosome translocation screening is therefore required. Current screening is performed by karyotyping; however, this relies on significant expertise and is limited in its ability to identify cryptic translocations. To address this problem, we developed a novel method for translocation screening in pigs and cattle using subtelomeric probes and multi-target fluorescence in situ hybridisation.

Probes designed to localise in the subtelomeric region of the p-arm and q-arm of each chromosome were directly labelled with FITC or Texas Red. These were subsequently applied to a ‘Multiprobe’ device, enabling simultaneous detection of each chromosome on a single slide - significantly shortening analysis time. Initial experiments led to the discovery of a series of incorrectly mapped regions in the porcine genome assembly, highlighting the importance of accurate physical mapping of newly sequenced genomes. Multiple porcine chromosome translocations were identified using this approach, including a cryptic translocation that was determined to have resulted in a loss of ~£20,000 to the breeder. This system therefore provides a robust and comprehensive method of screening for chromosomal abnormalities in agricultural species, with the benefit of potentially large cost savings to the industry.