In some cases, it is desirable to change the variability of a trait by selection. In pig breeding an example of such a trait is litter size, were especially extremely large litter sizes are less favoured because of higher risk of mortality in piglets and increased costs related to management of sows and piglets. Therefore, increasing uniformity of litter size would be advantageous. In a study that was just published in BMC Genomics, researchers of Wageningen UR found novel genomic regions that affect litter size and its variability.
There is evidence that the variability of traits is under genetic control meaning that some genotypes have higher or smaller variance, which would enable selection for increased uniformity. Very little is still known which genes are involved in controlling variability of traits. In this study, researchers performed a genome-wide association study for litter size and its variability in a Large White pig population. Several significant SNPs (single nucleotide polymorphism) were detected for litter size variability, for which also two promising candidate genes were found. The first candidate gene is coding a swine heat shock protein 90 (HSPCB = Hsp90), which is a well-studied gene stabilizing morphological traits in Drosophila (fly) and Arabidopsis (plant).
The second gene is VEGFA, which is activated in angiogenesis and vasculogenesis in the fetus. The genomic regions detected in this study can be used as indication for regions in the pig genome involved in maintaining low variability of litter size, but further studies are needed to identify the causative loci. Furthermore, detected SNPs can be used in genomic selection in pig breeding programs to reduce variability of litter size.