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Incorporating genomic annotation into single-step genomic prediction with imputed whole-genome sequence data
TENG Jin-yan, YE Shao-pan, GAO Ning, CHEN Zi-tao, DIAO Shu-qi, LI Xiu-jin, YUAN Xiao-long, ZHANG Hao, LI Jia-qi, ZHANG Xi-quan, ZHANG Zhe
2022, 21 (4): 1126-1136.   DOI: 10.1016/S2095-3119(21)63813-3
Abstract197)      PDF in ScienceDirect      
Single-step genomic best linear unbiased prediction (ssGBLUP) is now intensively investigated and widely used in livestock breeding due to its beneficial feature of combining information from both genotyped and ungenotyped individuals in the single model.  With the increasing accessibility of whole-genome sequence (WGS) data at the population level, more attention is being paid to the usage of WGS data in ssGBLUP.  The predictive ability of ssGBLUP using WGS data might be improved by incorporating biological knowledge from public databases.  Thus, we extended ssGBLUP, incorporated genomic annotation information into the model, and evaluated them using a yellow-feathered chicken population as the examples.  The chicken population consisted of 1 338 birds with 23 traits, where imputed WGS data including 5 127 612 single nucleotide polymorphisms (SNPs) are available for 895 birds.  Considering different combinations of annotation information and models, original ssGBLUP, haplotype-based ssGHBLUP, and four extended ssGBLUP incorporating genomic annotation models were evaluated.  Based on the genomic annotation (GRCg6a) of chickens, 3 155 524 and 94 837 SNPs were mapped to genic and exonic regions, respectively.  Extended ssGBLUP using genic/exonic SNPs outperformed other models with respect to predictive ability in 15 out of 23 traits, and their advantages ranged from 2.5 to 6.1% compared with original ssGBLUP.  In addition, to further enhance the performance of genomic prediction with imputed WGS data, we investigated the genotyping strategies of reference population on ssGBLUP in the chicken population.  Comparing two strategies of individual selection for genotyping in the reference population, the strategy of evenly selection by family (SBF) performed slightly better than random selection in most situations.  Overall, we extended genomic prediction models that can comprehensively utilize WGS data and genomic annotation information in the framework of ssGBLUP, and validated the idea that properly handling the genomic annotation information and WGS data increased the predictive ability of ssGBLUP.  Moreover, while using WGS data, the genotyping strategy of maximizing the expected genetic relationship between the reference and candidate population could further improve the predictive ability of ssGBLUP.  The results from this study shed light on the comprehensive usage of genomic annotation information in WGS-based single-step genomic prediction.

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Mitochondrial DNA diversity and origin of indigenous pigs in South China and their contribution to western modern pig breeds
WANG Chen, CHEN Yao-sheng, HAN Jian-lin, MO De-lin, LI Xiu-jin, LIU Xiao-hong
2019, 18 (10): 2338-2350.   DOI: 10.1016/S2095-3119(19)62731-0
Abstract139)      PDF in ScienceDirect      
Indigenous pigs in South China are valuable genetic resources with many specific and unique characters, which have played an important role in the establishment of some western modern pig breeds.  However, the origin and genetic diversity of indigenous pigs in South China have not been fully understood.  In the present study, we sequenced 534 novel mitochondrial DNA (mtDNA) D-loop and assembled 54 complete mitogenome sequences for all 17 indigenous pig breeds from Fujian, Guangdong, Guangxi and Hainan in South China.  These data were analyzed together with previously published homologous sequences relevant to this study.  We found that all 13 coding genes of the mitogenomes were under purifying selection, but ND1 had the most variable sites and CYTB contained the most non-synonymous SNPs.  Phylogenetic analysis showed that all indigenous pigs in South China were clustered into the D haplogroup with D1a1, D1b, D1c and D1e sub-haplogroups found to be dominant.  Haplotype and nucleotide diversities of D-loop sequences ranged from 0.427 to 0.899 and from 0.00342 to 0.00695, respectively, among which all pigs in Guangdong had the lowest diversity.  The estimates of pairwise FST, gene flow (Nm) and genetic distance (Da) indicated that most of these indigenous pig breeds differentiated from each other significantly (P<0.05).  Among the western modern breeds, Berkshire and Yorkshire had significant Asian matrilineal footprints from indigenous pigs in South China, especially the Spotted pigs distributed in Guangdong and Guangxi.  The neutrality test (Fu’s FS) indicated that indigenous pigs from Fujian and Guangxi had gone through recent population expansion events (P<0.05).  It is concluded that indigenous pigs in South China were most likely derived from the Mekong region and the middle and downstream regions of Yangtze River through Guangxi and Fujian.  Our findings provide a complete and in-depth insight on the origin and distribution pattern of maternal genetic diversity of indigenous pigs in South China.
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