X/XY/XYY mosaicism as a cause of subfertility in boars: a single case study

Classical, Molecular, and Genomic Cytogenetics of the Pig, a Clinical Perspective

The chromosomes of the domestic pig (Sus scrofa domesticus) are known to be prone to reciprocal chromosome translocations and other balanced chromosome rearrangements with concomitant fertility impairment of carriers. In response to the remarkable prevalence of chromosome rearrangements in swine herds, clinical cytogenetics laboratories have been established in several countries in order to screen young boars for chromosome rearrangements prior to service. At present, clinical cytogenetics laboratories typically apply classical cytogenetics techniques such as giemsa-trypsin (GTG)-banding to produce high-quality karyotypes and reveal large-scale chromosome ectopic exchanges. Further refinements to clinical cytogenetics practices have led to the implementation of molecular cytogenetics techniques such as fluorescent in-situ hybridization (FISH), allowing for rearrangements to be visualized and breakpoints refined using fluorescently labelled painting probes. The next-generation of clinical cytogenetics include the implementation of DNA microarrays, and next-generation sequencing (NGS) technologies such as DNA sequencing to better explore tentative genome architecture changes. The implementation of these cytogenomics techniques allow the genomes of rearrangement carriers to be deciphered at the highest resolution, allowing rearrangements to be detected; breakpoints to be delineated; and, most importantly, potential gene implications of those chromosome rearrangements to be interrogated. Clinical cytogenetics has become an integral tool in the livestock industry, identifying rearrangements and allowing breeders to make informed breeding decisions.

Breeding and Economic Aspects of Cytogenetic Screening Studies of Pigs Qualified for Reproduction

Cytogenetic monitoring allows the identification and early removal of pigs affected by inherited karyotype defects from breeding herds. These abnormalities cause developmental anomalies, considerably reducing the fertility (by several dozen to 100%) and performance parameters of breeding herds, resulting in substantial financial losses. This mainly concerns reciprocal translocations, typical of pigs, which are highly prevalent (about 0.46%), generally occur de novo, and normally result in low breeding soundness of the carriers. Due to the potential spontaneous occurrence of chromosomal aberrations and the rapid spread of these genetic defects in the population, especially under artificial insemination conditions, it is necessary to perform routine karyotype screening of animals qualified for reproduction. The cytogenetic screening program for young boars, carried out using continually refined diagnostic techniques, permits a precise and reliable karyotype assessment, identification of chromosomal abnormalities, and formulation of specific selection guidelines.