| 1. |
- Brandt, Monika, et al.
(author)
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Imputation-Based Fine-Mapping Suggests That Most QTL in an Outbred Chicken Advanced Intercross Body Weight Line Are Due to Multiple, Linked Loci
- 2017
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In: G3. - : Oxford University Press (OUP). - 2160-1836. ; 7:1, s. 119-128
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Journal article (peer-reviewed)abstract
- The Virginia chicken lines have been divergently selected for juvenile body weight for more than 50 generations. Today, the high- and low-weight lines show a >12-fold difference for the selected trait, 56-d body weight. These lines provide unique opportunities to study the genetic architecture of long-term, single-trait selection. Previously, several quantitative trait loci (QTL) contributing to weight differences between the lines were mapped in an F2-cross between them, and these were later replicated and fine-mapped in a nine-generation advanced intercross of them. Here, we explore the possibility to further increase the fine-mapping resolution of these QTL via a pedigree-based imputation strategy that aims to better capture the genetic diversity in the divergently selected, but outbred, founder lines. The founders of the intercross were high-density genotyped, and then pedigree-based imputation was used to assign genotypes throughout the pedigree. Imputation increased the marker density 20-fold in the selected QTL, providing 6911 markers for the subsequent analysis. Both single-marker association and multi-marker backward-elimination analyses were used to explore regions associated with 56-d body weight. The approach revealed several statistically and population structure independent associations and increased the mapping resolution. Further, most QTL were also found to contain multiple independent associations to markers that were not fixed in the founder populations, implying a complex underlying architecture due to the combined effects of multiple, linked loci perhaps located on independent haplotypes that still segregate in the selected lines.
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| 2. |
- Lillie, Mette, et al.
(author)
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Genome-wide standing variation facilitates long-term response to bidirectional selection for antibody response in chickens
- 2017
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In: BMC Genomics. - : Springer Science and Business Media LLC. - 1471-2164. ; 18
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Journal article (peer-reviewed)abstract
- BACKGROUND: Long-term selection experiments provide a powerful approach to gain empirical insights into adaptation, allowing researchers to uncover the targets of selection and infer their contributions to the mode and tempo of adaptation. Here we implement a pooled genome re-sequencing approach to investigate the consequences of 39 generations of bidirectional selection in White Leghorn chickens on a humoral immune trait: antibody response to sheep red blood cells.RESULTS: We observed wide genome involvement in response to this selection regime. Many genomic regions were highly differentiated resulting from this experimental selection regime, an involvement of up to 20% of the chicken genome (208.8 Mb). While genetic drift has certainly contributed to this, we implement gene ontology, association analysis and population simulations to increase our confidence in candidate selective sweeps. Three strong candidate genes, MHC, SEMA5A and TGFBR2, are also presented.CONCLUSIONS: The extensive genomic changes highlight the polygenic genetic architecture of antibody response in these chicken populations, which are derived from a common founder population, demonstrating the extent of standing immunogenetic variation available at the onset of selection.
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| 3. |
- Zan, Yanjun, et al.
(author)
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Artificial selection response due to polygenic adaptation from a multilocus, multiallelic genetic architecture
- 2017
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In: Molecular biology and evolution. - : Oxford University Press (OUP). - 0737-4038 .- 1537-1719. ; 34:10, s. 2678-2689
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Journal article (peer-reviewed)abstract
- The ability of a population to adapt to changes in their living conditions, whether in nature or captivity, often depends on polymorphisms in multiple genes across the genome. In-depth studies of such polygenic adaptations are difficult in natural populations, but can be approached using the resources provided by artificial selection experiments. Here, we dissect the genetic mechanisms involved in long-term selection responses of the Virginia chicken lines, populations that after 40 generations of divergent selection for 56-day body weight display a 9-fold difference in the selected trait. In the F15 generation of an intercross between the divergent lines, 20 loci explained >60% of the additive genetic variance for the selected trait. We focused particularly on fine-mapping seven major QTL that replicated in this population and found that only two fine-mapped to single, bi-allelic loci; the other five contained linked loci, multiple alleles or were epistatic. This detailed dissection of the polygenic adaptations in the Virginia lines provides a deeper understanding of the range of different genome-wide mechanisms that have been involved in these long-term selection responses. The results illustrate that the genetic architecture of a highly polygenic trait can involve a broad range of genetic mechanisms, and that this can be the case even in a small population bred from founders with limited genetic diversity.
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