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Detecting Signatures of Selection within the Dog Genome
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Medical Biochemistry and Microbiology.
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Deciphering the genetic basis of phenotypic diversity is one of the central aims of biological research. Domestic animals provide a unique opportunity for making substantial progress towards this goal. Intense positive selection has lead to a rich reservoir of phenotypes and underlying genotypes that can be interrogated using genetic tools to gain insight into the genetic basis of phenotypic diversity.

The dog is the most phenotypically diverse mammal. It was domesticated from the grey wolf 11-30,000 years ago. After domestication, a period of intense breeding has lead to the massive phenotypic diversity seen amongst dog breeds today. These two phases of strong positive selection at domestication and at breed creation are likely to have left their signature on the genome. In this thesis, we have analysed genome-wide patterns to detect genomic regions involved in selection in both of these phases. We used whole genome sequences from 60 dogs and 12 wolves, to detect dog domestication selective sweeps. We find evidence for genes involved in memory formation, neurotransmission and starch digestion.

To decipher the genetic signals underlying breed diversity, we used genome-wide genotype data from >170,000 SNPs in 509 dogs from 46 different breeds. We find evidence for genes under selection in many breeds, and only a few breeds. In addition, we identify novel sweeps underlying morphology and behavior.

Recombination can influence the configuration of alleles present on a haplotype, and can thus increase or decrease the efficiency of selection. The PRDM9 protein has been shown to be important for determining recombination hotspot locations in humans and other mammals, but of all the mammals studied so far the dog is the only one to have a non-functional PRDM9.

We used the genome-wide genotype data described above to characterise the fine scale recombination map in dogs. We find that recombination hotspots exist in dogs despite the absence of PRDM9. Moreover, we show that these hotspots are enriched for GC rich peaks and that these peaks are getting stronger over time. Our results show that the absence of PRDM9 has lead to the stabilisation of the recombination landscape in dogs.

 

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2013. , 38 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Medicine, ISSN 1651-6206 ; 938
Keyword [en]
dog, evolution, domestication, PRDM9, recombination, positive selection, selective sweep
National Category
Evolutionary Biology Bioinformatics and Systems Biology Genetics
Identifiers
URN: urn:nbn:se:uu:diva-209335ISBN: 978-91-554-8783-6 (print)OAI: oai:DiVA.org:uu-209335DiVA: diva2:656760
Public defence
2013-12-04, B42, BMC, Husargatan 3, Uppsala, 09:00 (English)
Opponent
Supervisors
Available from: 2013-11-13 Created: 2013-10-17 Last updated: 2014-01-23
List of papers
1. The genomic signature of dog domestication reveals adaptation to a starch-rich diet
Open this publication in new window or tab >>The genomic signature of dog domestication reveals adaptation to a starch-rich diet
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2013 (English)In: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 495, no 7441, 360-364 p.Article in journal (Refereed) Published
Abstract [en]

The domestication of dogs. was an important episode in the development of human civilization. The precise timing and location of this event is debated(1-5) and little is known about the genetic changes that accompanied the transformation of ancient wolves into domestic dogs. Here we conduct whole-genome resequencimg of dogs and wolves to identify 3.8 million genetic variants used to identify 36 genomic regions that probably represent targets for selection during dog domestication. Nineteen of these regions contain genes important in brain function, eight of which belong to nervous system development pathways and potentially underlie behavioural changes central to dog domestication(6). Ten genes with key roles in starch digestion and fat metabolism also show signals of selection. We identify candidate mutations in key genes and provide functional support for an increased starch digestion in dogs relative to wolves. Our results indicate that novel adaptations allowing the early ancestors of modern dogs to thrive on a diet rich in starch, relative to the carnivorous diet of wolves, constituted a crucial step in the early domestication of dogs.

National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-198620 (URN)10.1038/nature11837 (DOI)000316650500041 ()
Available from: 2013-04-22 Created: 2013-04-22 Last updated: 2017-12-06Bibliographically approved
2. High frequency derived alleles reveal signals of selection within the dog genome
Open this publication in new window or tab >>High frequency derived alleles reveal signals of selection within the dog genome
(English)Manuscript (preprint) (Other academic)
National Category
Evolutionary Biology
Identifiers
urn:nbn:se:uu:diva-209334 (URN)
Available from: 2013-10-17 Created: 2013-10-17 Last updated: 2014-01-23
3. Identification of genomic regions associated with phenotypic variation between dog breeds using selection mapping
Open this publication in new window or tab >>Identification of genomic regions associated with phenotypic variation between dog breeds using selection mapping
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2011 (English)In: PLoS Genetics, ISSN 1553-7404, Vol. 7, no 10, e1002316- p.Article in journal (Refereed) Published
Abstract [en]

The extraordinary phenotypic diversity of dog breeds has been sculpted by a unique population history accompanied by selection for novel and desirable traits. Here we perform a comprehensive analysis using multiple test statistics to identify regions under selection in 509 dogs from 46 diverse breeds using a newly developed high-density genotyping array consisting of >170,000 evenly spaced SNPs. We first identify 44 genomic regions exhibiting extreme differentiation across multiple breeds. Genetic variation in these regions correlates with variation in several phenotypic traits that vary between breeds, and we identify novel associations with both morphological and behavioral traits. We next scan the genome for signatures of selective sweeps in single breeds, characterized by long regions of reduced heterozygosity and fixation of extended haplotypes. These scans identify hundreds of regions, including 22 blocks of homozygosity longer than one megabase in certain breeds. Candidate selection loci are strongly enriched for developmental genes. We chose one highly differentiated region, associated with body size and ear morphology, and characterized it using high-throughput sequencing to provide a list of variants that may directly affect these traits. This study provides a catalogue of genomic regions showing extreme reduction in genetic variation or population differentiation in dogs, including many linked to phenotypic variation. The many blocks of reduced haplotype diversity observed across the genome in dog breeds are the result of both selection and genetic drift, but extended blocks of homozygosity on a megabase scale appear to be best explained by selection. Further elucidation of the variants under selection will help to uncover the genetic basis of complex traits and disease.

National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-162827 (URN)10.1371/journal.pgen.1002316 (DOI)000296665400017 ()22022279 (PubMedID)
Available from: 2011-12-05 Created: 2011-12-05 Last updated: 2014-09-19Bibliographically approved
4. Death of PRDM9 coincides with stabilization of the recombination landscape in the dog genome
Open this publication in new window or tab >>Death of PRDM9 coincides with stabilization of the recombination landscape in the dog genome
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2011 (English)In: Genome Research, ISSN 1088-9051, E-ISSN 1549-5469, Vol. 22, no 1, 51-63 p.Article in journal (Refereed) Published
Abstract [en]

Analysis of diverse eukaryotes has revealed that recombination events cluster in discrete genomic locations known as hotspots. In humans, a zinc-finger protein, PRDM9, is believed to initiate recombination in >40% of hotspots by binding to a specific DNA sequence motif. However, the PRDM9 coding sequence is disrupted in the dog genome assembly, raising questions regarding the nature and control of recombination in dogs. By analyzing the sequences of PRDM9 orthologs in a number of dog breeds and several carnivores, we show here that this gene was inactivated early in canid evolution. We next use patterns of linkage disequilibrium using more than 170,000 SNP markers typed in almost 500 dogs to estimate the recombination rates in the dog genome using a coalescent-based approach. Broad-scale recombination rates show good correspondence with an existing linkage-based map. Significant variation in recombination rate is observed on the fine scale, and we are able to detect over 4000 recombination hotspots with high confidence. In contrast to human hotspots, 40% of canine hotspots are characterized by a distinct peak in GC content. A comparative genomic analysis indicates that these peaks are present also as weaker peaks in the panda, suggesting that the hotspots have been continually reinforced by accelerated and strongly GC biased nucleotide substitutions, consistent with the long-term action of biased gene conversion on the dog lineage. These results are consistent with the loss of PRDM9 in canids, resulting in a greater evolutionary stability of recombination hotspots. The genetic determinants of recombination hotspots in the dog genome may thus reflect a fundamental process of relevance to diverse animal species.

National Category
Biochemistry and Molecular Biology Genetics
Identifiers
urn:nbn:se:uu:diva-162828 (URN)10.1101/gr.124123.111 (DOI)000298854200005 ()22006216 (PubMedID)
Funder
Swedish National Infrastructure for Computing (SNIC), b2009001Swedish Research CouncilEU, European Research Council
Available from: 2011-12-05 Created: 2011-12-05 Last updated: 2017-12-08Bibliographically approved

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Ratnakumar, Abhirami

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