A survey of functional genomic variation in domesticated chickens

Abstract

BackgroundDeleterious genetic variation can increase in frequency as a result of mutations, genetic drift, and genetic hitchhiking. Although individual effects are often small, the cumulative effect of deleterious genetic variation can impact population fitness substantially. In this study, we examined the genome of commercial purebred chicken lines for deleterious and functional variations, combining genotype and whole-genome sequence data.ResultsWe analysed over 22,000 animals that were genotyped on a 60 K SNP chip from four purebred lines (two white egg and two brown egg layer lines) and two crossbred lines. We identified 79 haplotypes that showed a significant deficit in homozygous carriers. This deficit was assumed to stem from haplotypes that potentially harbour lethal recessive variations. To identify potentially deleterious mutations, a catalogue of over 10 million variants was derived from 250 whole-genome sequenced animals from three purebred white-egg layer lines. Out of 4219 putative deleterious variants, 152 mutations were identified that likely induce embryonic lethality in the homozygous state. Inferred deleterious variation showed evidence of purifying selection and deleterious alleles were generally overrepresented in regions of low recombination. Finally, we found evidence that mutations, which were inferred to be evolutionally intolerant, likely have positive effects in commercial chicken populations.ConclusionsWe present a comprehensive genomic perspective on deleterious and functional genetic variation in egg layer breeding lines, which are under intensive selection and characterized by a small effective population size. We show that deleterious variation is subject to purifying selection and that there is a positive relationship between recombination rate and purging efficiency. In addition, multiple putative functional coding variants were discovered in selective sweep regions, which are likely under positive selection. Together, this study provides a unique molecular perspective on functional and deleterious variation in commercial egg-laying chickens, which can enhance current genomic breeding practices to lower the frequency of undesirable variants in the population.Electronic supplementary materialThe online version of this article (10.1186/s12711-018-0390-1) contains supplementary material, which is available to authorized users.

Deleterious alleles in the context of domestication, inbreeding, and selection

“…In addition, re‐sequence data from one commercial pig line ( N = 9) and three chicken lines ( N = 51;66;43) were obtained from (Derks et al., ; Derks, Megens et al. (submitted) and Derks et al., ) respectively.…”

“…1 European Nucleotide Archive (ENA) https://www.ebi.ac.uk/ena/data/view/PRJEB1683; 2 (Bosse et al., ) 3 (Yang et al., ) 4 (Derks et al., ) 5 (Ngeno, ) 6 (Ngeno et al., ) 7 (Derks et al., ), 8 (Derks, Megens et al. (submitted)).…”

“…(under review) is not accessible yet, the relevant vcf files are deposited into https://www.animalgenome.org/repository/pub/WUR2018.0809/. Genotype data from the same individuals were obtained from (Yang et al., ) and (Derks et al., ) for pigs and from (Derks et al., ) for chicken. The data obtained from Derks et al.…”

“…The data obtained from Derks et al. () was restricted but will be made available upon specific request to ensure repeatability is possible.…”

“…In addition, re-sequence data from one commercial pig line (N = 9) and three chicken lines (N = 51;66;43) were obtained from (Derks 1 European Nucleotide Archive (ENA) https://www.ebi.ac.uk/ena/data/view/PRJEB1683; 2 (Bosse et al, 2012) 3 (Yang et al, 2017) 4 (Derks et al, 2017) 5 (Ngeno, 2015) 6 7 (Derks et al, 2018), 8 (Derks, Megens et al (submitted)).…”