Insights into the architecture of human-induced polygenic selection in Duroc pigs

Background:As one of the most utilized commercial composite boar lines,Duroc pigs have been introduced to China and undergone strongly human-induced selection over the past decades.However,the efficiencies and limitations of previous breeding of Chinese Duroc pigs are largely understudied.The objective of this study was to uncover directional polygenic selection in the Duroc pig genome,and investigate points overlooked in the past breeding process.Results:Here,we utilized the Generation Proxy Selection Mapping(GPSM)on a dataset of 1067 Duroc pigs with 8,766,074 imputed SNPs.GPSM detected a total of 5649 putative SNPs actively under selection in the Chinese Duroc pig population,and the potential functions of the selection regions were mainly related to production,meat and carcass traits.Meanwhile,we observed that the allele frequency of variants related to teat number(NT)relevant traits was also changed,which might be influenced by genes that had pleiotropic effects.First,we identified the direction of selection on NT traits by G,and further pinpointed large-effect genomic regions associated with NT relevant traits by selection signature and GWAS.Combining results of NT relevant traits-specific selection signatures and GWAS,we found three common genome regions,which were overlapped with QTLs related to production,meat and carcass traits besides“teat number”QTLs.This implied that there were some pleiotropic variants underlying NT and economic traits.We further found that rs346331089 has pleiotropic effects on NT and economic traits,e.g.,litter size at weaning(LSW),litter weight at weaning(LWW),days to 100 kg(D100),backfat thickness at 100 kg(B100),and loin muscle area at 100 kg(L100)traits.Conclusions:The selected loci that we identified across methods displayed the past breeding process of Chinese Duroc pigs,and our findings could be used to inform future breeding decision.

Imputation from SNP chip to sequence: a case study in a Chinese indigenous chicken population

Background: Genome-wide association studies and genomic predictions are thought to be optimized by using whole-genome sequence(WGS) data. However, sequencing thousands of individuals of interest is expensive.Imputation from SNP panels to WGS data is an attractive and less expensive approach to obtain WGS data. The aims of this study were to investigate the accuracy of imputation and to provide insight into the design and execution of genotype imputation.Results: We genotyped 450 chickens with a 600 K SNP array, and sequenced 24 key individuals by whole genome re-sequencing. Accuracy of imputation from putative 60 K and 600 K array data to WGS data was 0.620 and 0.812 for Beagle, and 0.810 and 0.914 for FImpute, respectively. By increasing the sequencing cost from 24 X to 144 X, the imputation accuracy increased from 0.525 to 0.698 for Beagle and from 0.654 to 0.823 for FImpute. With fixed sequence depth(12 X), increasing the number of sequenced animals from 1 to 24, improved accuracy from 0.421 to0.897 for FImpute and from 0.396 to 0.777 for Beagle. Using optimally selected key individuals resulted in a higher imputation accuracy compared with using randomly selected individuals as a reference population for resequencing. With fixed reference population size(24), imputation accuracy increased from 0.654 to 0.875 for FImpute and from 0.512 to 0.762 for Beagle as the sequencing depth increased from 1 X to 12 X. With a given total cost of genotyping, accuracy increased with the size of the reference population for FImpute, but the pattern was not valid for Beagle, which showed the highest accuracy at six fold coverage for the scenarios used in this study.Conclusions: In conclusion, we comprehensively investigated the impacts of several key factors on genotype imputation. Generally, increasing sequencing cost gave a higher imputation accuracy. But with a fixed sequencing cost, the optimal imputation enhance the performance of WGP and GWAS. An optimal imputation strategy should take size of reference population, imputation algorithms, marker density, and population structure of the target population and methods to select key individuals into consideration comprehensively. This work sheds additional light on how to design and execute genotype imputation for livestock populations.

Multi-omics-data-assisted genomic feature markers preselection improves the accuracy of genomic prediction

Background:Presently,multi-omics data(e.g.,genomics,transcriptomics,proteomics,and metabolomics)are available to improve genomic predictors.Omics data not only offers new data layers for genomic prediction but also provides a bridge between organismal phenotypes and genome variation that cannot be readily captured at the genome sequence level.Therefore,using multi-omics data to select feature markers is a feasible strategy to improve the accuracy of genomic prediction.In this study,simultaneously using whole-genome sequencing(WGS)and gene expression level data,four strategies for single-nucleotide polymorphism(SNP)preselection were investigated for genomic predictions in the Drosophila Genetic Reference Panel.Results:Using genomic best linear unbiased prediction(GBLUP)with complete WGS data,the prediction accuracies were 0.208±0.020(0.181±0.022)for the startle response and 0.272±0.017(0.307±0.015)for starvation resistance in the female(male)lines.Compared with GBLUP using complete WGS data,both GBLUP and the genomic feature BLUP(GFBLUP)did not improve the prediction accuracy using SNPs preselected from complete WGS data based on the results of genome-wide association studies(GWASs)or transcriptome-wide association studies(TWASs).Furthermore,by using SNPs preselected from the WGS data based on the results of the expression quantitative trait locus(eQTL)mapping of all genes,only the startle response had greater accuracy than GBLUP with the complete WGS data.The best accuracy values in the female and male lines were 0.243±0.020 and 0.220±0.022,respectively.Importantly,by using SNPs preselected based on the results of the eQTL mapping of significant genes from TWAS,both GBLUP and GFBLUP resulted in great accuracy and small bias of genomic prediction.Compared with the GBLUP using complete WGS data,the best accuracy values represented increases of 60.66%and 39.09%for the starvation resistance and 27.40%and 35.36%for startle response in the female and male lines,respectively.Conclusions:Overall,multi-omics data can assist genomic feature preselection and improve the performance of genomic prediction.The new knowledge gained from this study will enrich the use of multi-omics in genomic prediction.