A genome scan of recent positive selection signatures in three sheep populations

Domesticated sheep have been exposed to artificial selection for the production of fiber, meat, and milk as well as to natural selection. Such selections are likely to have imposed distinctive selection signatures on the sheep genome. Therefore, detecting selection signatures across the genome may help elucidate mechanisms of selection and pinpoint candidate genes of interest for further investigation. Here, detection of selection signatures was conducted in three sheep breeds, Sunite （n=66）, German Mutton （n=159）, and Dorper （n=93）, using the Illumina OvineSNP50 Genotyping BeadChip array. Each animal provided genotype information for 43 273 autosomal single nucleotide polymorphisms （SNPs）. We adopted two complementary haplotype-based statistics of relative extended haplotype homozygosity （REHH） and the cross-popu- lation extended haplotype homozygosity （XP-EHH） tests. In total, 707,755, and 438 genomic regions subjected to positive selection were identified in Sunite, German Mutton, and Dorper sheep, respectively, and 42 of these regions were detected using both REHH and XP-EHH analyses. These genomic regions harbored many important genes, which were enriched in gene ontology terms involved in muscle development, growth, and fat metabolism. Fourteen of these genomic regions overlapped with those identified in our previous genome-wide association studies, further indicating that these genes under positive selection may underlie growth developmental traits. These findings contribute to the identification of candidate genes of interest and aid in understanding the evolutionary and biological mechanisms for controlling complex traits in Chinese and western sheep.

Genome-wide scan for selection signatures based on whole-genome re-sequencing in Landrace and Yorkshire pigs

We performed a genome-wide scan to detect selection signatures that showed evidence of positive selection in the domestication process by re-sequencing the whole genomes of Landrace and Yorkshire pigs.Fifteen annotated elements with 13 associated genes were identified using the Z-transformed FST(Z(FST))method,and 208 annotated elements with 140 associated genes were identified using the Z-transformed heterozygosity(ZHp)method.The functional analysis and the results of previous studies showed that most of the candidate genes were associated with basic metabolism,disease resistance,cellular processes,and biochemical signals,and several were related to body morphology and organs.They included PPP3CA,which plays an essential role in the transduction of intracellular Ca2+-mediated signals,and WWTR1,which plays a pivotal role in organ size control and tumor suppression.These results suggest that genes associated with body morphology were subject to selection pressure during domestication,whereas genes involved in basic metabolism and disease resistance were subject to selection during artificial breeding.Our findings provide new insights into the potential genetic variation of phenotypic diversity in different pig breeds and will help to better understand the selection effects of modern breeding in Landrace and Yorkshire pigs.

Development of Genome-Wide Scan for Selection Signature in Farm Animals

Identifying targets of positive selection in farm animals has, until recently, been frustratingly slow, relying on the analysis of individual candidate genes. Genomics, however, has provided the necessary resources to systematically interrogate the entire genome for signatures of selection. This review described important recent results derived from the application of genome-wide scan to the study of genetic changes in farm animals. These included findings of regions of the genome that showed breed differentiation, evidence of selective sweeps within individual genomes and signatures of demographic events. Particular attention is focused on the study of the implications for domestication. To date, sixteen genome-wide scans for recent or ongoing positive selection have been performed in farm animals. A key challenge is to begin synthesizing these newly constructed maps of selection into a coherent narrative of animal breed evolutionary history and derive a deeper mechanistic understanding of how animal populations improve or evolve. The major insights from the surveyed studies are highlighted and directions for future study are suggested.

Integration of genome-wide association study and selection signatures reveals genetic determinants for skeletal muscle production traits in an F2 chicken population

Improving the production of broiler chicken meat has been a goal of broiler breeding programs worldwide for many years. However, the genetic architectures of skeletal muscle production traits in chickens have not yet been fully elucidated. In the present study, a total of 519 F_(2) birds, derived from a cross of Arbor Acres broiler and Baier layer, were re-sequenced(26 F_(0) individuals were re-sequenced at a 10-fold depth;519 F_(2) individuals were re-sequenced at a 3-fold depth) and the coupling of genome-wide association study(GWAS) and selection signatures(FST(fixation index) and θπ(nucleotide diversity)) was carried out to pinpoint the associated loci and genes that contribute to pectoral muscle weight(PMW) and thigh muscle weight(TMW). A total of 7 890 258 single nucleotide polymorphisms(SNPs) remained to be analyzed after quality control and imputation. The integration of GWAS and selection signature analyses revealed that genetic determinants responsible for skeletal muscle production traits were mainly localized on chromosomes 1(168.95–172.43 Mb) and 4(74.37–75.23 Mb). A total of 17 positional candidate genes(PCGs)(LRCH1, CDADC1, CAB39 L, LOC112531568, LOC112531569, FAM124 A, FOXO1, NBEA, GPALPP1, RUBCNL, ARL11, KPNA3, LHFP, GBA3, LOC112532426, KCNIP4, and SLIT2) were identified in these regions. In particular, KPNA3 and FOXO1 were the most promising candidates for meat production in chickens. These findings will help enhance our understanding of the genetic architecture of chicken muscle production traits, and the significant SNPs identified could be promising candidates for integration into practical breeding programs such as genome-wide selection(GS) to improve the meat yield of chickens.

Genomic signatures of selection,local adaptation and production type characterisation of East Adriatic sheep breeds

Background The importance of sheep breeding in the Mediterranean part of the eastern Adriatic has a long tradition since its arrival during the Neolithic migrations.Sheep production system is extensive and generally carried out in traditional systems without intensive systematic breeding programmes for high uniform trait production(carcass,wool and milk yield).Therefore,eight indigenous Croatian sheep breeds from eastern Adriatic treated here as metapopulation(EAS),are generally considered as multipurpose breeds(milk,meat and wool),not specialised for a particular type of production,but known for their robustness and resistance to certain environmental conditions.Our objective was to identify genomic regions and genes that exhibit patterns of positive selection signatures,decipher their biological and productive functionality,and provide a"genomic"characterization of EAS adaptation and determine its production type.Results We identified positive selection signatures in EAS using several methods based on reduced local variation,linkage disequilibrium and site frequency spectrum(eROHi,iHS,nSL and CLR).Our analyses identified numerous genomic regions and genes(e.g.,desmosomal cadherin and desmoglein gene families)associated with environmental adaptation and economically important traits.Most candidate genes were related to meat/production and health/immune response traits,while some of the candidate genes discovered were important for domestication and evolutionary processes(e.g.,HOXa gene family and FSIP2).These results were also confirmed by GO and QTL enrichment analysis.Conclusions Our results contribute to a better understanding of the unique adaptive genetic architecture of EAS and define its productive type,ultimately providing a new opportunity for future breeding programmes.At the same time,the numerous genes identified will improve our understanding of ruminant(sheep)robustness and resistance in the harsh and specific Mediterranean environment.

Whole-genome resequencing reveals recent signatures of selection in five populations of largemouth bass(Micropterus salmoides)

Largemouth bass(Micropterus salmoides) is an economically important fish species in North America, Europe, and China. Various genetic improvement programs and domestication processes have modified its genome sequence through selective pressure, leaving nucleotide signals that can be detected at the genomic level. In this study,we sequenced 149 largemouth bass fish, including protospecies(imported from the US) and improved breeds(four domestic breeding populations from China). We detected genomic regions harboring certain genes associated with improved traits, which may be useful molecular markers for practical domestication, breeding, and selection. Subsequent analyses of genetic diversity and population structure revealed that the improved breeds have undergone more rigorous genetic changes. Through selective signal analysis, we identified hundreds of putative selective sweep regions in each largemouth bass line. Interestingly, we predicted 103 putative candidate genes potentially subjected to selection,including several associated with growth(psst1 and grb10), early development(klf9, sp4, and sp8), and immune traits(pkn2, sept2, bcl6, and ripk2). These candidate genes represent potential genomic landmarks that could be used to improve important traits of biological and commercial interest. In summary, this study provides a genome-wide map of genetic variations and selection footprints in largemouth bass, which may benefit genetic studies and accelerate genetic improvement of this economically important fish.

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.

Whole-genome resequencing reveals molecular imprints of anthropogenic and natural selection in wild and domesticated sheep

The abundance of domesticated sheep varieties and phenotypes is largely the result of long-term natural and artificial selection. However, there is limited information regarding the genetic mechanisms underlying phenotypic variation induced by the domestication and improvement of sheep. In this study, to explore genomic diversity and selective regions at the genome level, we sequenced the genomes of 100 sheep across 10 breeds and combined these results with publicly available genomic data from 225 individuals, including improved breeds, Chinese indigenous breeds,African indigenous breeds, and their Asian mouflon ancestor. Based on population structure, the domesticated sheep formed a monophyletic group,while the Chinese indigenous sheep showed a clear geographical distribution trend. Comparative genomic analysis of domestication identified several selective signatures, including IFI44 and IFI44L genes and PANK2 and RNF24 genes, associated with immune response and visual function.Population genomic analysis of improvement demonstrated that candidate genes of selected regions were mainly associated with pigmentation,energy metabolism, and growth development.Furthermore, the IFI44 and IFI44L genes showed a common selection signature in the genomes of 30domesticated sheep breeds. The IFI44 c. 54413058C>G mutation was selected for genotyping and population genetic validation. Results showed that the IFI44 polymorphism was significantly associated with partial immune traits. Our findings identified the population genetic basis of domesticated sheep at the whole-genome level, providing theoretical insights into the molecular mechanism underlying breed characteristics and phenotypic changes during sheep domestication and improvement.

Genome-wide detection of selective signatures in a Duroc pig population

The Duroc pig has high adaptability and feeding efficiency, making it one of the most popular pig breeds worldwide. Over long periods of natural and artificial selection, genetic footprints, i.e., selective signatures, were left in the genome. In this study, a Duroc pig population （n=715） was genotyped with the Porcine SNP60K Bead Chip and the GeneSeek Genomic Profiler （GGP） Porcine Chip. The relative extended haplotype homozygosity （REHH） method was used for selective signature detection in a subset of the population （n=368）, selected to represent a balanced family structure. In total, 154 significant core regions were detected as selective signatures （,P〈0.01）, some of which overlap with previously reported quantitative trait loci associated with several economically important traits, including average daily gain and backfat thickness. Genome annotation for these significant core regions revealed a variety of interesting candidate genes including GATA3, TAF3, ATP5C1, and FGFI. These genes were functionally related to anterior/posterior pattern specification, phosphatidylinositol 3-kinase signaling, embryonic skeletal system morphogenesis, and oxidation-reduction processes. This research provides knowledge for the study of selection mechanisms and breeding practices in Duroc and other pigs.

Whole-genome resequencing of Hu sheep identifies candidate genes associated with agronomic traits

The phenotypic diversity resulting from artificial or natural selection of sheep has made a significant contribution to human civilization.Hu sheep are a local sheep breed unique to China with high reproductive rates and rapid growth.Genomic selection signatures have been widely used to investigate the genetic mechanisms underlying phenotypic variation in livestock.Here,we conduct whole-genome sequencing of 207 Hu sheep and compare them with the wild ancestors of domestic sheep(Asiatic mouflon)to investigate the genetic characteristics and selection signatures of Hu sheep.Based on six signatures of selection approaches,we detect genomic regions containing genes related to reproduction(BMPR1B,BMP2,PGFS,CYP19,CAMK4,GGT5,and GNAQ),vision(ALDH1A2,SAG,and PDE6B),nervous system(NAV1),and immune response(GPR35,SH2B2,PIK3R3,and HRAS).Association analysis with a population of 1299 Hu sheep reveals that those missense mutations in the GPR35(GPR35 g.952651 A>G;GPR35 g.952496 C>T)and NAV1(NAV1 g.84216190 C>T;NAV1 g.84227412 G>A)genes are significantly associated(P<0.05)with immune and growth traits in Hu sheep,respectively.This research offers unique insights into the selection characteristics of Hu sheep and facilitates further genetic improvement and molecular investigations.

Multi-omic Analyses Shed Light on The Genetic Control of High-altitude Adaptation in Sheep

Sheep were domesticated in the Fertile Crescent and then spread globally,where they have been encountering various environmental conditions.The Tibetan sheep has adapted to high altitudes on the Qinghai-Tibet Plateau over the past 3000 years.To explore genomic variants associated with high-altitude adaptation in Tibetan sheep,we analyzed Illumina short-reads of 994 whole genomes representing∼60 sheep breeds/populations at varied altitudes,PacBio High fidelity(HiFi)reads of 13 breeds,and 96 transcriptomes from 12 sheep organs.Association testing between the inhabited altitudes and 34,298,967 variants was conducted to investigate the genetic architecture of altitude adaptation.Highly accurate HiFi reads were used to complement the current ovine reference assembly at the most significantly associatedβ-globin locus and to validate the presence of two haplotypes A and B among 13 sheep breeds.The haplotype A carried two homologous gene clusters:(1)HBE1,HBE2,HBB-like,and HBBC,and(2)HBE1-like,HBE2-like,HBB-like,and HBB;while the haplotype B lacked the first cluster.The high-altitude sheep showed highly frequent or nearly fixed haplotype A,while the low-altitude sheep dominated by haplotype B.We further demonstrated that sheep with haplotype A had an increased hemoglobin–O_(2) affinity compared with those carrying haplotype B.Another highly associated genomic region contained the EGLN1 gene which showed varied expression between high-altitude and low-altitude sheep.Our results provide evidence that the rapid adaptive evolution of advantageous alleles play an important role in facilitating the environmental adaptation of Tibetan sheep.

Characterizing structural variants based on graph-genotyping provides insights into pig domestication and local adaption

Structural variants(SVs),such as deletions(DELs)and insertions(INSs),contribute substantially to pig genetic diversity and phenotypic variation.Using a library of SVs discovered from long-read primary assemblies and short-read sequenced genomes,we map pig genomic SVs with a graph-based method for re-genotyping SVs in 402 genomes.Our results demonstrate that those SVs harboring specific trait-associated genes may greatly shape pig domestication and local adaptation.Further characterization of SVs reveals that some population-stratified SVs may alter the transcription of genes by affecting regulatory elements.We identify that the genotypes of two DELs(296-bp DEL,chr7:52,172,101e52,172,397;278-bp DEL,chr18:23,840,143 e23,840,421)located in muscle-specific enhancers are associated with the expression of target genes related to meat quality(FSD2)and muscle fiber hypertrophy(LMOD2 and WASL)in pigs.Our results highlight the role of SVs in domestic porcine evolution,and the identified candidate functional genes and SVs are valuable resources for future genomic research and breeding programs in pigs.

BGVD:An Integrated Database for Bovine Sequencing Variations and Selective Signatures

Next-generation sequencing has yielded a vast amount of cattle genomic data for global characterization of population genetic diversity and identification of genomic regions under natural and artificial selection.However,efficient storage,querying,and visualization of such large datasets remain challenging.Here,we developed a comprehensive database,the Bovine Genome Variation Database(BGVD).It provides six main functionalities:gene search,variation search,genomic signature search,Genome Browser,alignment search tools,and the genome coordinate conversion tool.BGVD contains information on genomic variations comprising^60.44 M SNPs,~6.86 M indels,76,634 CNV regions,and signatures of selective sweeps in 432 samples from modern cattle worldwide.Users can quickly retrieve distribution patterns of these variations for 54 cattle breeds through an interactive source of breed origin map,using a given gene symbol or genomic region for any of the three versions of the bovine reference genomes(ARS-UCD1.2,UMD3.1.1,and Btau5.0.1).Signals of selection sweep are displayed as Manhattan plots and Genome Browser tracks.To further investigate and visualize the relationships between variants and signatures of selection,the Genome Browser integrates all variations,selection data,and resources,from NCBI,the UCSC Genome Browser,and Animal QTLdb.Collectively,all these features make the BGVD a useful archive for in-depth data mining and analyses of cattle biology and cattle breeding on a global scale.BGVD is publicly available at http://animal.nwsuaf.edu.cn/BosVar.

GGVD:A goat genome variation database for tracking the dynamic evolutionary process of selective signatures and ancient introgressions

Understanding the evolutionary history and adaptive process depends on the knowledge that we can acquire from both ancient and modern genomic data.With the availability of a deluge of whole-genome sequencing data from ancient and modern goat samples,a user-friendly database making efficient reuse of these important resources is needed.Here,we use the genomes of 208 modern domestic goats,24 bezoars,46 wild ibexes,and 82 ancient goats to present a comprehensive goat genome variation database(GGVD).GGVD hosts a total of~41.44 million SNPs,~5.14 million indels,6,193 selected loci,and 112 introgression regions.Users can freely visualize the frequency of genomic variations in geographical maps,selective sweeps in interactive tables,Manhattan plots,or line charts,as well as the heatmap patterns of the SNP genotype.Ancient data can be shown in haplotypes to track the state of genetic variants of selection and introgression events in the early,middle,and late stages.For facilitating access to sequence features,the UCSC Genome Browser,BLAT,BLAST,Lift Over,and pcadapt are also integrated into GGVD.GGVD will be a convenient tool for population genetic studies and molecular marker designing in goat breeding programs,and it is publicly available at http://animal.nwsuaf.edu.cn/Goat Var.

A Chromosome-level Genome Assembly of Wild Castor Provides New Insights into Its Adaptive Evolution in Tropical Desert

Wild castor grows in the high-altitude tropical desert of the African Plateau,a region known for high ultraviolet radiation,strong light,and extremely dry condition.To investigate the potential genetic basis of adaptation to both highland and tropical deserts,we generated a chromosome-level genome sequence assembly of the wild castor accession WT05,with a genome size of 316 Mb,a scaffold N50 of 31.93 Mb,and a contig N50 of 8.96 Mb,respectively.Compared with cultivated castor and other Euphorbiaceae species,the wild castor exhibits positive selection and gene family expansion for genes involved in DNA repair,photosynthesis,and abiotic stress responses.Genetic variations associated with positive selection were identified in several key genes,such as LIG1,DDB2,and RECG1,involved in nucleotide excision repair.Moreover,a study of genomic diversity among wild and cultivated accessions revealed genomic regions containing selection signatures associated with the adaptation to extreme environments.The identification of the genes and alleles with selection signatures provides insights into the genetic mechanisms underlying the adaptation of wild castor to the high-altitude tropical desert and would facilitate direct improvement of modern castor varieties.