No abstract

Transmission ratio distortion (TRD) is defined as the allele transmission deviation from the heterozygous parent to the offspring from the expected Mendelian genotypic frequencies. Although TRD can be a confounding factor in genetic mapping studies, this phenomenon remains mostly unknown in pigs, particularly in traditional breeds (i.e., the Iberian pig). We aimed to describe the maternal TRD prevalence and its genomic distribution in two Iberian varieties. Genotypes from a total of 247 families (dam and offspring) of Entrepelado (n = 129) and Retinto (n = 118) Iberian varieties were analyzed. The offspring were sired by both ungenotyped purebred Retinto and Entrepelado Iberian boars, regardless of the dam variety used. After quality control, 16,246 single-nucleotide polymorphisms (SNPs) in the Entrepelado variety and 9744 SNPs in the Retinto variety were analyzed. Maternal TRD was evaluated by a likelihood ratio test under SNP-by-SNP, adapting a previous model solved by Bayesian inference. Results provided 68 maternal TRD loci (TRDLs) in the Entrepelado variety and 24 in the Retinto variety (q < 0.05), with mostly negative TRD values, increasing the transmission of the minor allele. In addition, both varieties shared ten common TRDLs. No strong evidence of biological effects was found in genes with TRDLs. However, some biological processes could be affected by TRDLs, such as embryogenesis at different levels and lipid metabolism. These findings could provide useful insight into the genetic mechanisms to improve the swine industry, particularly in traditional breeds.

Several variants in the KIT, PAX3 and MITF genes have previously been associated with white markings in horses. In this study, we examined eight variants of these genes in 70 Menorca Purebred horses (PRMe, only black solid-coloured horses) and 70 Spanish Purebred horses (PRE, different coat colour patterns) that were scored for the extent of white markings. A maximum-likelihood chi-square test, logistic regression model and ridge regression analyses showed that a missense mutation (p.Arg682His) in KIT was associated with white facial markings (P < 0.05) and with total white markings (P < 0.05) in PRMe horses. The relative contribution of this variant to white markings in PRMe horses was estimated at 47.6% (head) and 43.4% (total score). In PRE horses, this variant was also associated with hindlimb scores (P < 0.05) with a relative contribution of 41.2%. The g.20147039C>T intronic variant located 29.9 kb downstream from the transcription start site of the MITF gene was associated with less white markings on forelimbs (P < 0.05) in PRMe horses, with a relative contribution of 63.9%, whereas in PRE horses this variant was associated with white facial markings (P < 0.05), with a relative contribution of 63.9%. No significant associations were found for PAX3 variants in these breeds. These results show that KIT and MITF variants are involved in the white marking patterns of both PRMe and PRE horses, providing breeders with an opportunity to use genetic testing to aid in breeding for their desired level of white markings.

No abstract

Eye temperature assessed with infrared thermography is an adequate tool for stress level assessment in sport horses’ competitions having a moderate heritability. Serotonin and dopamine signal transduction-linked gene variants have been associated with anxiety-related traits in several species. In this study we examined the association between 10 gene variants in BDNF, COMT, HTR1A, TPH2 and SLC6A4 genes (and the haplotypes at SLC6A4 gene) with stress level (measured with eye temperature and heart rate) in 270 animals, 135 Spanish Trotter Horses (STH) participating in trotting races and 135 ‘Pura Raza Español’ (PRE) horses in dressage. Association analyses were performed using a unified mixed model (counting for population structure and individual relatedness) for the whole population and for each horse breed. The g.43865600G &gt; A intronic gene variant located 11.0 kb downstream from the transcription start site of SLC6A4 gene was associated with an increase in eye temperature before competition with a relative contribution of this gene variant of 38.8% (P = 0.001), 31.8% just after (P = 0.001) and 29.8% 2 h after the competition (P = 0.003). In STH, the g.43865600G &gt; A gene variant showed the same association with eye temperature before (P = 0.001, contribution 27.2%), just after (P = 0.0003, 29.0%) and after the competition (P = 0.002, 17.5%); and the c.*111G &gt; A gene variant located at the 3′UTR region of COMT gene was associated with eye temperature 2 h after the competition (P = 0.001, 22.3%). These results showed that SLC6A4 and COMT gene variants are associated with stress level measured as eye temperature increase during competitions, and may be promising tools for genetic testing against resistance at high stress levels in trotter horses.