The Y chromosome plays key roles in male fertility and reflects the evolutionary history of paternal lineages. Here, we present a de novo genome assembly of the Hu sheep with the first draft assembly of ovine Y chromosome (oMSY), using nanopore sequencing and Hi-C technologies. The oMSY that we generated spans 10.6 Mb from which 775 Y-SNPs were identified by applying a large panel of whole genome sequences from worldwide sheep and wild Iranian mouflons. Three major paternal lineages (HY1a, HY1b and HY2) were defined across domestic sheep, of which HY2 was newly detected. Surprisingly, HY2 forms a monophyletic clade with the Iranian mouflons and is highly divergent from both HY1a and HY1b. Demographic analysis of Y chromosomes, mitochondrial and nuclear genomes confirmed that HY2 and the maternal counterpart of lineage C represented a distinct wild mouflon population in Iran that diverge from the direct ancestor of domestic sheep, the wild mouflons in Southeastern Anatolia. Our results suggest that wild Iranian mouflons had introgressed into domestic sheep and thereby introduced this Iranian mouflon specific lineage carrying HY2 to both East Asian and Africa sheep populations.

Structural variations (SVs) are a major contributor to genetic diversity and phenotypic variations, but their prevalence and functions in domestic animals are largely unexplored. Here we generated high-quality genome assemblies for 15 individuals from genetically diverse sheep breeds using Pacific Biosciences (PacBio) high-fidelity sequencing, discovering 130.3 Mb nonreference sequences, from which 588 genes were annotated. A total of 149,158 biallelic insertions/deletions, 6531 divergent alleles, and 14,707 multiallelic variations with precise breakpoints were discovered. The SV spectrum is characterized by an excess of derived insertions compared to deletions (94,422 vs. 33,571), suggesting recent active LINE expansions in sheep. Nearly half of the SVs display low to moderate linkage disequilibrium with surrounding single-nucleotide polymorphisms (SNPs) and most SVs cannot be tagged by SNP probes from the widely used ovine 50K SNP chip. We identified 865 population-stratified SVs including 122 SVs possibly derived in the domestication process among 690 individuals from sheep breeds worldwide. A novel 168-bp insertion in the 5′ untranslated region (5′ UTR) ofHOXB13is found at high frequency in long-tailed sheep. Further genome-wide association study and gene expression analyses suggest that this mutation is causative for the long-tail trait. In summary, we have developed a panel of high-quality de novo assemblies and present a catalog of structural variations in sheep. Our data capture abundant candidate functional variations that were previously unexplored and provide a fundamental resource for understanding trait biology in sheep.

The takin (Budorcas taxicolor) is a large bovid herbivore, belonging to the subfamily Caprinae. The number of takins was estimated to be only 7000-12,000 (Cheng et al., 2020) and it has been listed as vulnerable by the International Union for Conservation of Nature (IUCN) (Zeng & Song, 2002). It was divided into four subspecies according to physiological characteristics and geographical location (Wu, 1986). Qinling takin (Bu. t. bedfordi) and Sichuan takin (Bu. t. tibetana) are confined to China, while the Mishmi takin (Bu. t. taxicolor) has a distribution from the Gaoligong Mountains in northwestern Yunnan province, China, to India and Myanmar (Wu, 1986). In addition, Bhutan takin (Bu. t. whieti) is found in Bhutan and the Yarlung Zangbo River in Tibet, China (Li et al., 2003). Qinling takin (Bu. t. bedfordi), also known as golden takin, is mainly distributed in the Qinling Mountains of China (Figure 1a;Li, Qiu, et al., 2021).Compared to other Caprinae, the morphology, ecological traits and G-banded karyotype of takin were found to be similar to muskox (Ovibos moschatus) (Pasitschniak-Arts et al., 1994). However, analysis of mitochondrial cytochrome b (Cytb) sequences showed that

Low‐coverage whole genome sequencing (lcWGS) has great potential to effectively genotype large‐scale population and to provide solid data for imputation; however, the time for imputation needs to be optimized. There is also no publicly available reference panel for whole genome selection in cattle. Here, we proposed a combination of Beagle v5.4 for phasing and GLIMPSE2 for imputation, which is fast and accurate for cattle lcWGS data. Furthermore, we established a multi‐breed reference panel with 61.8 million SNPs based on 2976 worldwide cattle, of which 1766 were bulls, by evaluating diversity and the size of the reference panel. The evaluation of imputation accuracy was conducted using new reference panel for both lcWGS and Bovine BeadChip data. The average concordance rate in Holstein was 99.6%, 99.6%, and 99.5% for 1X, 0.5X, and 0.1X lcWGS data, 99.5% and 99.0% for 777K and 50K chip data, and it was 98.8% for 1X lcWGS data in Simmental. We further investigated the factors affecting the imputation accuracy of lcWGS data and discovered that segmental duplication, structural variant, and guanine‐cytosine content were the top three factors. Interestingly, we found that 10 regions longer than 0.5 Mb showed low imputation accuracy enriched with immune function, such as 96.1% characterized genes in regions of chromosome 10, with more attention being paid on downstream immune‐related analysis. Our study provides the workflow of imputing lcWGS data and establishes the first high‐quality cattle reference panel with free access, which provides a resource to conduct subsequent large‐scale genome‐wide association studies and genomic selection.

Climate change, especially weather extremes like extreme cold or extreme hot, is a major challenge for global livestock. One of the animal breeding goals for sustainable livestock production should be to breed animals with excellent climate adaptability. Indigenous livestock and poultry are well adapted to the local climate, and they are good resources to study the genetic footprints and mechanism of the resilience to weather extremes. In order to identify selection signatures and genes that might be involved in hot adaptation in indigenous chickens from different tropical climates, we conducted a genomic analysis of 65 indigenous chickens that inhabit different climates. Several important unique positively selected genes (PSGs) were identified for each local chicken group by the cross-population extended haplotype homozygosity (XP-EHH). These PSGs, verified by composite likelihood ratio, genetic differentiation index, nucleotide diversity, Tajima’s D, and decorrelated composite of multiple signals, are related to nerve regulation, vascular function, immune function, lipid metabolism, kidney development, and function, which are involved in thermoregulation and hot adaptation. However, one common PSG was detected for all three tropical groups of chickens via XP-EHH but was not confirmed by other five types of selective sweep analyses. These results suggest that the hot adaptability of indigenous chickens from different tropical climate regions has evolved in parallel by taking different pathways with different sets of genes. The results from our study have provided reasonable explanations and insights for the rapid adaptation of chickens to diverse tropical climates and provide practical values for poultry breeding.

The takin (Budorcas taxicolor) is one of the largest bovid herbivores across caprinae subfamily. The takin is at high risk of extinction, however, its taxonomic status is still unclear. In this study, we constructed the first reference genome of B. taxicolor using PacBio long High-Fidelity reads and Hi-C technology. The assembled genome is ~2.95 Gb with a contig N50 of 68.05 Mb and a scaffold N50 of 101.27 Mb, which were anchored onto 25+XY chromosomes. Compared to the common ancestral karyotype of bovidae (2n=60), we found the takin (2n=52) experienced four chromosome fusions and one large translocation. We also found that the takin was most closely related to muskox, not other caprinae species. Further, we re-sequenced nine golden takins from the main distribution area, Qinling Mountains, and identified 3.3 million SNPs. The genetic diversity of takin was very low (θπ=0.00028 and heterozygosity=0.00038), which was among the lowest detected in the domestic and wild mammals. We also found takin genomes showed high inbreeding coefficient (FROH=0.217) suggesting severe inbreeding depression. The genome analysis show that the effective population size of takins declined significantly from ~100,000 years ago. Our results provide valuable information for protection of takins and insights into its evolution.

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