BackgroundPolymorphisms underlying complex traits often explain a small part (less than 1 %) of the phenotypic variance (σ2 P). This makes identification of mutations underling complex traits difficult and usually only a subset of large-effect loci are identified. One approach to identify more loci is to increase sample size of experiments but here we propose an alternative. The aim of this paper is to use secondary phenotypes for genetically simple traits during the QTL discovery phase for complex traits. We demonstrate this approach in a dairy cattle data set where the complex traits were milk production phenotypes (fat, milk and protein yield; fat and protein percentage in milk) measured on thousands of individuals while secondary (potentially genetically simpler) traits are detailed milk composition traits (measurements of individual protein abundance, mineral and sugar concentrations; and gene expression).ResultsQuantitative trait loci (QTL) were identified using 11,527 Holstein cattle with milk production records and up to 444 cows with milk composition traits. There were eight regions that contained QTL for both milk production and a composition trait, including four novel regions. One region on BTAU1 affected both milk yield and phosphorous concentration in milk. The QTL interval included the gene SLC37A1, a phosphorous antiporter. The most significant imputed sequence variants in this region explained 0.001 σ2 P for milk yield, and 0.11 σ2 P for phosphorus concentration. Since the polymorphisms were non-coding, association mapping for SLC37A1 gene expression was performed using high depth mammary RNAseq data from a separate group of 371 lactating cows. This confirmed a strong eQTL for SLC37A1, with peak association at the same imputed sequence variants that were most significant for phosphorus concentration. Fitting any of these variants as covariables in the association analysis removed the QTL signal for milk production traits. Plausible causative mutations in the casein complex region were also identified using a similar strategy.ConclusionsMilk production traits in dairy cows are typical complex traits where polymorphisms explain only a small portion of the phenotypic variance. However, here we show that these mutations can have larger effects on secondary traits, such as concentrations of minerals, proteins and sugars in the milk, and expression levels of genes in mammary tissue. These larger effects were used to successfully map variants for milk production traits. Genetically simple traits also provide a direct biological link between possible causal mutations and the effect of these mutations on milk production.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-016-3175-3) contains supplementary material, which is available to authorized users.

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A PCR-RFLP method to confirm the identification of four Pelodiscus sinensis strains (Taihu Lake strain, Taiwan strain, Yellow River strain and Japanese strain) was developed and evaluated. In this study, we sequenced and analyzed the partial sequences of mitochondrial NADH4, COX I and NADH5-NADH6 genes of 60 individuals from the four P. sinensis strains. Bgl I, Hpa II and Cla I were selected for cutting NADH4, COX I and NADH5-NADH6 PCR products, respectively, and each strain has its unique restriction band patterns. The result showed that all the 140 samples tested can be correctly identified based on the combination of the three digested fragments pattern. This study provides an effective method to distinguish the four main strains of P. sinensis.

A novel well-dispersed Pd@HHSS catalyst was synthesized by reduction of Pd(OAc)2 immobilized on HHSS we reported. When the ratios of Pd/SiO2 were 5 : 100 and 10 : 100, the Pd nanoparticles size was about 5–10 nm. The Pd@HHSS catalyst (Pd/SiO2 = 10 : 100) showed high catalytic activity in Suzuki-reaction with yields of 91–99% and the catalyst is reusable after four successive cycles without obvious loss of catalytic activity.

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