Genomic insights into the population structure and history of the Irish Travellers

Scoping review on Physical Health Conditions in Irish Travellers (Mincéiri)

OBJECTIVE

The objective of this scoping review was to collate physical health conditions in Mincéiri-Irish Travellers.

DESIGN

Scoping review.

SEARCH STRATEGY AND CHARTING METHOD

MEDLINE/PubMed, EMBASE, PEDro, AMED, CINAHL, PsycINFO, SCOPUS as well as reports and grey literature were searched for primary data reporting physical health conditions of Irish Travellers up to 4 April 2023. Data was extracted, described and organised meaningfully into tables according to reported physical health conditions.

ELIGIBILITY CRITERIA

The population was Travellers. The concept referred to physical health conditions. The context was Irish Travellers based in any location or setting. Exclusion criteria was data/research other than primary data relating to physical health conditions of Irish Travellers.

RESULTS

From 198 citations generated from the database search, 11 unique studies (20 reports) were included in this scoping review, including n=7397 participants. Driven by the data, physical health conditions were categorised into cardiovascular diseases, respiratory diseases, injuries/musculoskeletal/arthritic disorders, genetic disorders and gut/bowel conditions. This review showed that the metabolic syndrome, asthma, bronchitis, tuberculosis and intentional injuries were 2-3 times more prevalent in Irish Travellers compared with the background population. Genetic conditions were also described in a proportion of Travellers.

CONCLUSIONS

Overall, Irish Travellers experience a disproportionate burden of physical health conditions compared with background populations. Healthcare providers need to be aware of the unique physical health burden experienced by many Irish Travellers. Multifaceted strategies are needed to improve the health profile of this vulnerable and marginalised group.

The Newfoundland and Labrador mosaic founder population descends from an Irish and British diaspora from 300 years ago

The founder population of Newfoundland and Labrador (NL) is a unique genetic resource, in part due to its geographic and cultural isolation, where historical records describe a migration of European settlers, primarily from Ireland and England, to NL in the 18th and 19th centuries. Whilst its historical isolation, and increased prevalence of certain monogenic disorders are well appreciated, details of the fine-scale genetic structure and ancestry of the population are lacking. Understanding the genetic origins and background of functional, disease causing, genetic variants would aid genetic mapping efforts in the Province. Here, we leverage dense genome-wide SNP data on 1,807 NL individuals to reveal fine-scale genetic structure in NL that is clustered around coastal communities and correlated with Christian denomination. We show that the majority of NL European ancestry can be traced back to the south-east and south-west of Ireland and England, respectively. We date a substantial population size bottleneck approximately 10-15 generations ago in NL, associated with increased haplotype sharing and autozygosity. Our results reveal insights into the population history of NL and demonstrate evidence of a population conducive to further genetic studies and biomarker discovery.

Presentations of self-harm and suicide-related ideation among the Irish Traveller indigenous population to hospital emergency departments: evidence from the National Clinical Programme for self-harm

PURPOSE

Previous research has examined the suicide risk of the Irish Traveller population, but less is known about self-harm and suicidal ideation among this ethnic minority group, which are established risk factors for suicide. The aim of the current study was to compare the presentation-based self-harm and suicide-related ideation of Traveller to non-Traveller patients and describe any ethnic disparities in the aftercare of their presentation.

METHODS

Data were obtained from the service improvement database of an Irish dedicated national programme for the assessment of those presenting to emergency departments (EDs) due to self-harm and suicide-related ideation. Presentation data from 24 EDs were analysed and Poisson regression was used to assess the age-sex-adjusted relative risk of hospital-presenting self-harm and suicide-related ideation.

RESULTS

24,473 presentations were recorded with 3% of the presentations made by Irish Travellers. Female Traveller patients had 3·04 (95% CI 2·51-3·68) higher risk for suicide-related ideation and 3·85 (95% CI 3·37-4·41) for self-harm, compared to white Irish female patients. Male Traveller patients had 4·46 (95% CI 3·86-5·16) higher risk for suicide-related ideation and 5·43 (95% CI 4·75-6·21) higher rates for self-harm. The highest rate ratios for self-harm were observed among older Traveller patients [male: 9·23 (95% CI 5·93-14·39); female: 6·79 (95% CI 4·37-10·57)]. A higher proportion of Traveller patients requested no next of kin involvement, compared to other ethnicities.

CONCLUSIONS

Given that Irish Travellers are at higher risk of self-harm and suicide-related ideation presentations compared to other ethnic groups, EDs should be viewed as an important suicide intervention point.

Case series: Psychosocial challenges of female youth within the Irish Travelling community

BACKGROUND

The Irish Travelling community are an ethnic minority group known for their distinct identity, traditions and language. Although this group has its roots in Ireland, they are marginalised and discriminated against by every part of Irish society. Irish Travellers are a group who are vulnerable to exclusion and experience health, economic and educational inequalities. Young female Irish Travellers in Ireland are highly susceptible to mental illnesses which makes the engagement of this ethnic group by healthcare services important.

AIMS

To review the cases of three female adolescents from the Irish Travelling community living in Ireland with a focus on their psycho-social difficulties. Complete a literature review, to complement and inform the three cases reviewed, on the socio-cultural and mental health challenges which effect adolescent females in the Irish Travelling community.

METHODS

Case series with literature search and review of relevant published articles using a keyword search of databases PubMed, PsycINFO and HSE protocols and reports. Hand searching of relevant references utilised. Informed signed consent obtained from each patient attending child and adolescent services in Ireland. Signed parental consent also obtained. Written consent obtained due to the use of patient history and assessments in the case series.

RESULTS

Adolescent females within the Irish Travelling community encounter particular difficulties within the moral constraints and expectations of this community. They encounter specific issues including mental illness, sexual stigma, domestic violence and limitations to the role of women. The three cases outlined give representative examples of the challenges faced by adolescent females within the Travelling community.

CONCLUSIONS

Psychiatric services need to be aware of this vulnerable group and focus on the recognition of their needs within the context of their community.

Gypsy, Traveller and Roma experiences, views and needs in palliative and end of life care: a systematic literature review and narrative synthesis

BACKGROUND

Gypsy, Traveller and Roma communities are known to experience health inequalities. There has been little focus on palliative care in these communities despite the well-recognised inequalities of access to palliative care in other minority ethnic groups.

METHODS

Systematic review and thematic analysis of the current evidence concerning palliative care experiences, views and needs of Gypsy, Traveller and Roma communities. Medline, Embase, Emcare, CINAHL, PsycINFO, Web of Science, Scopus, AMED, Global Health, Psychological and Behavioural Sciences Collection and BNI were searched up to November 2020, alongside author and citation searching. NHS England, Hospice UK, National Audit Office and OpenGrey were searched as grey literature sources. Gough's 'Weight of Evidence' framework was used for quality appraisal.

RESULTS

Thirteen papers from eight studies were included in the synthesis. Although there was variation between communities, three overarching and inter-related themes were identified. (1) Strong family and community values include a preference for healthcare to be provided from within the community, duty to demonstrate respect by attending the bedside and illness as a community problem with decision-making extending beyond the patient. (2) Distinct health beliefs regarding superstitions around illness, personal care, death rituals and bereavement. (3) Practical barriers to non-community healthcare provision include communication difficulties, limited awareness of and access to services, tensions between patients and healthcare professionals and lack of training in delivering culturally appropriate care.

CONCLUSION

A wide range of factors influence Gypsy, Traveller and Roma community access to palliative care. Community diversity requires sensitive and highly individualised approaches to patient care.

PROSPERO REGISTRATION NUMBER

42019147905.

Investigative genetic genealogy: Current methods, knowledge and practice

Investigative genetic genealogy (IGG) has emerged as a new, rapidly growing field of forensic science. We describe the process whereby dense SNP data, commonly comprising more than half a million markers, are employed to infer distant relationships. By distant we refer to degrees of relatedness exceeding that of first cousins. We review how methods of relationship matching and SNP analysis on an enlarged scale are used in a forensic setting to identify a suspect in a criminal investigation or a missing person. There is currently a strong need in forensic genetics not only to understand the underlying models to infer relatedness but also to fully explore the DNA technologies and data used in IGG. This review brings together many of the topics and examines their effectiveness and operational limits, while suggesting future directions for their forensic validation. We further investigated the methods used by the major direct-to-consumer (DTC) genetic ancestry testing companies as well as submitting a questionnaire where providers of forensic genetic genealogy summarized their operation/services. Although most of the DTC market, and genetic genealogy in general, has undisclosed, proprietary algorithms we review the current knowledge where information has been discussed and published more openly.

Barriers and Considerations for Diagnosing Rare Diseases in Indigenous Populations

Advances in omics and specifically genomic technologies are increasingly transforming rare disease diagnosis. However, the benefits of these advances are disproportionately experienced within and between populations, with Indigenous populations frequently experiencing diagnostic and therapeutic inequities. The International Rare Disease Research Consortium (IRDiRC) multi-stakeholder partnership has been advancing toward the vision of all people living with a rare disease receiving an accurate diagnosis, care, and available therapy within 1 year of coming to medical attention. In order to further progress toward this vision, IRDiRC has created a taskforce to explore the access barriers to diagnosis of rare genetic diseases faced by Indigenous peoples, with a view of developing recommendations to overcome them. Herein, we provide an overview of the state of play of current barriers and considerations identified by the taskforce, to further stimulate awareness of these issues and the passage toward solutions. We focus on analyzing barriers to accessing genetic services, participating in genomic research, and other aspects such as concerns about data sharing, the handling of biospecimens, and the importance of capacity building.

Microbiome and health implications for ethnic minorities after enforced lifestyle changes

Modern lifestyles increase the risk of chronic diseases, in part by modifying the microbiome, but the health effects of lifestyles enforced on ethnic minorities are understudied^1-3. Lifestyle affects the microbiome early in life, when the microbiome is assembled and the immune system is undergoing maturation^4-6. Moreover, the influence of lifestyle has been separated from genetic and geographic factors by studies of genetically similar populations and ethnically distinct groups living in the same geographic location^7-11. The lifestyle of Irish Travellers, an ethnically distinct subpopulation, changed with legislation in 2002 that effectively ended nomadism and altered their living conditions. Comparative metagenomics of gut microbiomes shows that Irish Travellers retain a microbiota similar to that of non-industrialized societies. Their microbiota is associated with non-dietary factors and is proportionately linked with risk of microbiome-related metabolic disease. Our findings suggest there are microbiome-related public health implications when ethnic minorities are pressured to change lifestyles.

Genetic structure and admixture in sheep from terminal breeds in the United States

Selection for performance in diverse production settings has resulted in variation across sheep breeds worldwide. Although sheep are an important species to the United States, the current genetic relationship among many terminal sire breeds is not well characterized. Suffolk, Hampshire, Shropshire and Oxford (terminal) and Rambouillet (dual purpose) sheep (n = 248) sampled from different flocks were genotyped using the Applied Biosystems Axiom Ovine Genotyping Array (50K), and additional Shropshire sheep (n = 26) using the Illumina Ovine SNP50 BeadChip. Relationships were investigated by calculating observed heterozygosity, inbreeding coefficients, eigenvalues, pairwise Wright’s F_ST estimates and an identity by state matrix. The mean observed heterozygosity for each breed ranged from 0.30 to 0.35 and was consistent with data reported in other US and Australian sheep. Suffolk from two different regions of the United States (Midwest and West) clustered separately in eigenvalue plots and the rectangular cladogram. Further, divergence was detected between Suffolk from different regions with Wright’s F_ST estimate. Shropshire animals showed the greatest divergence from other terminal breeds in this study. Admixture between breeds was examined using admixture, and based on cross‐validation estimates, the best fit number of populations (clusters) was K = 6. The greatest admixture was observed within Hampshire, Suffolk, and Shropshire breeds. When plotting eigenvalues, US terminal breeds clustered separately in comparison with sheep from other locations of the world. Understanding the genetic relationships between terminal sire breeds in sheep will inform us about the potential applicability of markers derived in one breed to other breeds based on relatedness.

Are Gypsy Roma Traveller communities indigenous and would identification as such better address their public health needs?

INTRODUCTION

Across Europe, large numbers of Gypsy Roma Traveller communities experience significant health inequities such as higher morbidity, mortality and infant mortality. This health inequity is perpetuated by wider determinants such as a lower social status, lower educational attainment and substandard accommodation. This is not dissimilar to other indigenous peoples, even though many Gypsy Roma Traveller communities are not identified as indigenous.

METHODS

This article presents contemporary literature and research alongside the internationally agreed principles of indigenous peoples, examining similarities between Gypsy Roma Traveller communities and other indigenous peoples.

RESULTS

We argue that Gypsy Roma Traveller communities could be recognised as indigenous in terms of the internationally agreed principles of indigeneity and shared experiences of health inequity, colonisation and cultural genocide. Doing so would enable a more robust public health strategy and development of public health guidelines that take into account their cultural views and practices.

CONCLUSION

Recognising Gypsy Roma Traveller communities in this way is important, especially concerning public health, as formal recognition of indigeneity provides certain rights and protection that can be used to develop appropriate public health strategies. Included within this are more nuanced approaches to promoting health, which focus on strengths and assets rather than deficit constructs that can perpetuate problematising of these communities.

Refractive error and visual impairment in Ireland schoolchildren

Aim

To report refractive error prevalence and visual impairment in Republic of Ireland (henceforth 'Ireland') schoolchildren.

Methods

The Ireland Eye Study examined 1626 participants (881 boys, 745 girls) in two age groups, 6–7 years (728) and 12–13 years (898), in Ireland between June 2016 and January 2018. Participating schools were selected by stratified random sampling, representing a mix of school type (primary/postprimary), location (urban/rural) and socioeconomic status (disadvantaged/advantaged). Examination included monocular logarithm of the minimum angle of resolution (logMAR) presenting visual acuity (with spectacles if worn) and cycloplegic autorefraction (1% Cyclopentolate Hydrochloride). Parents completed a questionnaire to ascertain participants’ lifestyle.

Results

The prevalence of myopia (spherical equivalent refraction (SER): ≤−0.50 D), hyperopia (SER: ≥+2.00 D) and astigmatism (≤−1.00 DC) among participants aged 6–7 years old was 3.3%, 25% and 19.2%, respectively, and among participants aged 12–13 years old was 19.9%, 8.9% and 15.9%, respectively. Astigmatic axes were predominately with-the-rule. The prevalence of ‘better eye’ presenting visual impairment (≥0.3 logMAR, with spectacles, if worn) was 3.7% among younger and 3.4% among older participants. Participants in minority groups (Traveller and non-white) were significantly more likely to present with presenting visual impairment in the ‘better eye’.

Conclusions

The Ireland Eye Study is the first population-based study to report on refractive error prevalence and visual impairment in Ireland. Myopia prevalence is similar to comparable studies of white European children, but the levels of presenting visual impairment are markedly higher than those reported for children living in Northern Ireland, suggesting barriers exist in accessing eye care.

Haplotype Sharing Provides Insights into Fine-Scale Population History and Disease in Finland

Finland provides unique opportunities to investigate population and medical genomics because of its adoption of unified national electronic health records, detailed historical and birth records, and serial population bottlenecks. We assembled a comprehensive view of recent population history (≤100 generations), the timespan during which most rare-disease-causing alleles arose, by comparing pairwise haplotype sharing from 43,254 Finns to that of 16,060 Swedes, Estonians, Russians, and Hungarians from geographically and linguistically adjacent countries with different population histories. We find much more extensive sharing in Finns, with at least one ≥ 5 cM tract on average between pairs of unrelated individuals. By coupling haplotype sharing with fine-scale birth records from more than 25,000 individuals, we find that although haplotype sharing broadly decays with geographical distance, there are pockets of excess haplotype sharing; individuals from northeast Finland typically share several-fold more of their genome in identity-by-descent segments than individuals from southwest regions. We estimate recent effective population-size changes through time across regions of Finland, and we find that there was more continuous gene flow as Finns migrated from southwest to northeast between the early- and late-settlement regions than was dichotomously described previously. Lastly, we show that haplotype sharing is locally enriched by an order of magnitude among pairs of individuals sharing rare alleles and especially among pairs sharing rare disease-causing variants. Our work provides a general framework for using haplotype sharing to reconstruct an integrative view of recent population history and gain insight into the evolutionary origins of rare variants contributing to disease.

Clinical, biochemical, and genetic features of four patients with short-chain enoyl-CoA hydratase (ECHS1) deficiency

Short-chain enoyl-CoA hydratase (SCEH or ECHS1) deficiency is a rare inborn error of metabolism caused by biallelic mutations in the gene ECHS1 (OMIM 602292). Clinical presentation includes infantile-onset severe developmental delay, regression, seizures, elevated lactate, and brain MRI abnormalities consistent with Leigh syndrome (LS). Characteristic abnormal biochemical findings are secondary to dysfunction of valine metabolism. We describe four patients from two consanguineous families (one Pakistani and one Irish Traveler), who presented in infancy with LS. Urine organic acid analysis by GC/MS showed increased levels of erythro-2,3-dihydroxy-2-methylbutyrate and 3-methylglutaconate (3-MGC). Increased urine excretion of methacrylyl-CoA and acryloyl-CoA related metabolites analyzed by LC-MS/MS, were suggestive of SCEH deficiency; this was confirmed in patient fibroblasts. Both families were shown to harbor homozygous pathogenic variants in the ECHS1 gene; a c.476A > G (p.Gln159Arg) ECHS1variant in the Pakistani family and a c.538A > G, p.(Thr180Ala) ECHS1 variant in the Irish Traveler family. The c.538A > G, p.(Thr180Ala) ECHS1 variant was postulated to represent a Canadian founder mutation, but we present SNP genotyping data to support Irish ancestry of this variant with a haplotype common to the previously reported Canadian patients and our Irish Traveler family. The presence of detectable erythro-2,3-dihydroxy-2-methylbutyrate is a nonspecific marker on urine organic acid analysis but this finding, together with increased excretion of 3-MGC, elevated plasma lactate, and normal acylcarnitine profile in patients with a Leigh-like presentation should prompt consideration of a diagnosis of SCEH deficiency and genetic analysis of ECHS1. ECHS1 deficiency can be added to the list of conditions with 3-MGA.

Insular Celtic population structure and genomic footprints of migration

Previous studies of the genetic landscape of Ireland have suggested homogeneity, with population substructure undetectable using single-marker methods. Here we have harnessed the haplotype-based method fineSTRUCTURE in an Irish genome-wide SNP dataset, identifying 23 discrete genetic clusters which segregate with geographical provenance. Cluster diversity is pronounced in the west of Ireland but reduced in the east where older structure has been eroded by historical migrations. Accordingly, when populations from the neighbouring island of Britain are included, a west-east cline of Celtic-British ancestry is revealed along with a particularly striking correlation between haplotypes and geography across both islands. A strong relationship is revealed between subsets of Northern Irish and Scottish populations, where discordant genetic and geographic affinities reflect major migrations in recent centuries. Additionally, Irish genetic proximity of all Scottish samples likely reflects older strata of communication across the narrowest inter-island crossing. Using GLOBETROTTER we detected Irish admixture signals from Britain and Europe and estimated dates for events consistent with the historical migrations of the Norse-Vikings, the Anglo-Normans and the British Plantations. The influence of the former is greater than previously estimated from Y chromosome haplotypes. In all, we paint a new picture of the genetic landscape of Ireland, revealing structure which should be considered in the design of studies examining rare genetic variation and its association with traits.

A recent genetic study of the UK (People of the British Isles; PoBI) expanded our understanding of population history of the islands, using newly-developed, powerful techniques that harness the rich information embedded in chunks of genetic code called haplotypes. These methods revealed subtle regional diversity across the UK, and, using genetic data alone, timed key migration events into southeast England and Orkney. We have extended these methods to Ireland, identifying regional differences in genetics across the island that adhere to geography at a resolution not previously reported. Our study reveals relative western diversity and eastern homogeneity in Ireland owing to a history of settlement concentrated on the east coast and longstanding Celtic diversity in the west. We show that Irish Celtic diversity enriches the findings of PoBI; haplotypes mirror geography across Britain and Ireland, with relic Celtic populations contributing greatly to haplotypic diversity. Finally, we used genetic information to date migrations into Ireland from Europe and Britain consistent with historical records of Viking and Norman invasions, demonstrating the signatures of these migrations the on modern Irish genome. Our findings demonstrate that genetic structure exists in even small isolated populations, which has important implications for population-based genetic association studies.

Catalogue of inherited disorders found among the Irish Traveller population

Background Irish Travellers are an endogamous, nomadic, ethnic minority population mostly resident on the island of Ireland with smaller populations in Europe and the USA. High levels of consanguinity result in many rare autosomal recessive disorders. Due to founder effects and endogamy, most recessive disorders are caused by specific homozygous mutations unique to this population. Key clinicians and scientists with experience in managing rare disorders seen in this population have developed a de facto advisory service on differential diagnoses to consider when faced with specific clinical scenarios.

Objective(s) To catalogue all known inherited disorders found in the Irish Traveller population.

Methods We performed detailed literature and database searches to identify relevant publications and the disease mutations of known genetic disorders found in Irish Travellers.

Results We identified 104 genetic disorders: 90 inherited in an autosomal recessive manner; 13 autosomal dominant and one a recurring chromosomal duplication.

Conclusion We have collated our experience of inherited disorders found in the Irish Traveller population to make it publically available through this publication to facilitate a targeted genetic approach to diagnostics in this ethnic group.

Runs of homozygosity: windows into population history and trait architecture

Long runs of homozygosity (ROH) arise when identical haplotypes are inherited from each parent and thus a long tract of genotypes is homozygous. Cousin marriage or inbreeding gives rise to such autozygosity; however, genome-wide data reveal that ROH are universally common in human genomes even among outbred individuals. The number and length of ROH reflect individual demographic history, while the homozygosity burden can be used to investigate the genetic architecture of complex disease. We discuss how to identify ROH in genome-wide microarray and sequence data, their distribution in human populations and their application to the understanding of inbreeding depression and disease risk.

The Irish DNA Atlas: Revealing Fine-Scale Population Structure and History within Ireland

The extent of population structure within Ireland is largely unknown, as is the impact of historical migrations. Here we illustrate fine-scale genetic structure across Ireland that follows geographic boundaries and present evidence of admixture events into Ireland. Utilising the 'Irish DNA Atlas', a cohort (n = 194) of Irish individuals with four generations of ancestry linked to specific regions in Ireland, in combination with 2,039 individuals from the Peoples of the British Isles dataset, we show that the Irish population can be divided in 10 distinct geographically stratified genetic clusters; seven of 'Gaelic' Irish ancestry, and three of shared Irish-British ancestry. In addition we observe a major genetic barrier to the north of Ireland in Ulster. Using a reference of 6,760 European individuals and two ancient Irish genomes, we demonstrate high levels of North-West French-like and West Norwegian-like ancestry within Ireland. We show that that our 'Gaelic' Irish clusters present homogenous levels of ancient Irish ancestries. We additionally detect admixture events that provide evidence of Norse-Viking gene flow into Ireland, and reflect the Ulster Plantations. Our work informs both on Irish history, as well as the study of Mendelian and complex disease genetics involving populations of Irish ancestry.

Weighted likelihood inference of genomic autozygosity patterns in dense genotype data

Background

Genomic regions of autozygosity (ROA) arise when an individual is homozygous for haplotypes inherited identical-by-descent from ancestors shared by both parents. Over the past decade, they have gained importance for understanding evolutionary history and the genetic basis of complex diseases and traits. However, methods to infer ROA in dense genotype data have not evolved in step with advances in genome technology that now enable us to rapidly create large high-resolution genotype datasets, limiting our ability to investigate their constituent ROA patterns.

Methods

We report a weighted likelihood approach for inferring ROA in dense genotype data that accounts for autocorrelation among genotyped positions and the possibilities of unobserved mutation and recombination events, and variability in the confidence of individual genotype calls in whole genome sequence (WGS) data.

Results

Forward-time genetic simulations under two demographic scenarios that reflect situations where inbreeding and its effect on fitness are of interest suggest this approach is better powered than existing state-of-the-art methods to infer ROA at marker densities consistent with WGS and popular microarray genotyping platforms used in human and non-human studies. Moreover, we present evidence that suggests this approach is able to distinguish ROA arising via consanguinity from ROA arising via endogamy. Using subsets of The 1000 Genomes Project Phase 3 data we show that, relative to WGS, intermediate and long ROA are captured robustly with popular microarray platforms, while detection of short ROA is more variable and improves with marker density. Worldwide ROA patterns inferred from WGS data are found to accord well with those previously reported on the basis of microarray genotype data. Finally, we highlight the potential of this approach to detect genomic regions enriched for autozygosity signals in one group relative to another based upon comparisons of per-individual autozygosity likelihoods instead of inferred ROA frequencies.

Conclusions

This weighted likelihood ROA inference approach can assist population- and disease-geneticists working with a wide variety of data types and species to explore ROA patterns and to identify genomic regions with differential ROA signals among groups, thereby advancing our understanding of evolutionary history and the role of recessive variation in phenotypic variation and disease.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-017-4312-3) contains supplementary material, which is available to authorized users.