Low-resolution genetic analysis suggests a common Irish origin between the settled and the Traveller populations. What is not known, however, is the extent of population structure within the Irish Travellers, the time of divergence from the general Irish population, or the extent of autozygosity.
Using a sample of 50 Irish Travellers, European Roma, settled Irish, British and European or world-wide individuals, we demonstrate evidence for population substructure within the Irish Traveller population, and estimate a time of divergence before the Great Famine of — The levels of autozygosity and distinct Irish origins have implications for disease mapping within Ireland, while the population structure and divergence inform on social history. The Irish Travellers are a community within Ireland, consisting of between 29,—40, individuals, representing 0.
They are traditionally nomadic, moving around rural Ireland and providing seasonal labour, as well as participating in horse-trading and tin-smithing 2. Despite this change in lifestyle, the Traveller community remains tight-knit but also socially isolated.
The population has its own language 4 , known as Shelta, of which Cant and Gammon are dialects. There is a lack of documentary evidence informing on the history of the Irish Traveller population 5 , 6. As a result, their origins are a source of considerable debate, with no single origin explanation being widely accepted. It has been suggested that the Irish Travellers are a hybrid population between settled Irish and Romani gypsies, due to the similarities in their nomadic lifestyle.
The Irish Traveller population may even pre-date these events, and represent Celtic or pre-Celtic isolates 4. These models of ethnogenesis are not necessarily mutually exclusive, and the Irish Traveller population may have multiple sources of origin with a shared culture.
Consanguineous marriages are common within the Irish Traveller community 7 , 8. Small, isolated and endogamous populations such as the Travellers are also more prone to the effects of genetic drift. The isolation and consanguinity have in turn led to an increased prevalence of recessive diseases 7 , 9 , 10 , with higher incidences of diseases such as transferase-deficient galactosaemia 11 , 12 , and Hurler syndrome 13 observed in the Traveller population relative to the settled Irish.
However, the extent of autozygosity within the population has yet to be quantified; as a result it is unknown how homozygous the population is compared to other, better-studied, isolated European populations.
Previous work into the genetics of the Irish Traveller population has been conducted on datasets of relatively low genetic resolution. A recent study used blood groups to investigate the population history of the Irish Travellers 2.
Multivariate analysis of genotype data across 12 red blood cell loci in Irish Travellers suggested that the population clustered closely with the settled Irish to the exclusion of the Roma.
They did, however, appear divergent from the settled Irish. The authors attributed the source of such divergence to genetic drift - but were unable to determine whether any such drift was due to a founder effect, or sustained endogamy. Using dense, genome-wide, SNP datasets which provide much greater resolution than genetic systems studied in the Travellers to date, we set out to i describe the genetic structure within the Traveller population, ii the relationship between the Irish Travellers and other European populations, iii estimate the time of divergence between the Travellers and settled Irish, and iv the levels of autozygosity within the Irish Traveller population.
In order to investigate the genetic relationship between the Irish Travellers and neighbouring populations we performed fineStructure analysis on Irish Travellers, settled Irish from a subset of the Trinity Student dataset 14 , and British from a subset of the POBI dataset A subset of the datasets were used in this analysis as we were primarily interested in the placing of the Irish Travellers within the context of Britain and Ireland, not the full structure found within Britain and Ireland.
The results are presented in Fig. A The first and second components of principal component analysis of the haplotype-based co-ancestry matrix produced by fineStructure analysis. Individual clusters are indicated by colour and shape. Individual Irish Travellers are indicated with black bordered shapes, with cluster shown in Legend. B The full fineStructure tree with the highest posterior probability, with cluster size and name, and broad branches shown.
These three individuals report full, or partial, English gypsie ancestry, a distinct and separate travelling population in Britain.
One individual is found within the Ireland 1 cluster, and two are found within the Ireland 2 cluster. Traveller individuals within the Ireland 2 cluster report recent settled ancestry, and we have no such genealogical data on the individual grouped within the Ireland 1 cluster. Given their mixed ancestry, these individuals were excluded from subsequent F st , f 3 , and divergence estimate work.
The remaining 28 Irish Travellers in the fineStructure analysis were arranged into four clusters. These clusters were grouped on two separate branches Fig.
The branch with clusters Traveller 3 and 4 , forms an outgroup to the rest of the settled Irish and Irish Traveller clusters. This pattern is also repeated in the PCA Fig. Having identified distinct genetic groups of Irish Travellers, we investigated the correlation with Irish Traveller sociolinguistic features, specifically Shelta dialect, and Rathkeale residence Fig.
S2B ,C, respectively. The majority of the Gammon speakers were members of clusters Traveller 1 and 2. All of Traveller 1 consisted of Gammon speakers. The majority of clusters Traveller 3 and 4 consisted of Cant speakers, where all but one individual, for whom language identity is unknown, of Traveller 4 were Cant speakers. We found that only clusters Traveller 1 and 2 contain any Rathkeale Travellers, where 4 out of 5 individuals in Traveller 2 are Rathkeale Travellers.
For this analysis we used a subset of the European Multiple Sclerosis dataset consisting of three northern European Norway, Finland and Germany , two southern European Italy and Spain , and a neighbouring population France.
Shown are the ancestry components per individual for the two groups of Irish Travellers Group A and Group B , settled Irish, British, and European populations; modelling for 4 to 6 ancestral populations. Although at lower values of k the Irish Travellers generally resemble the settled Irish profile Fig. S3 , at higher values of k two components are found to be enriched within the population.
S3 suggests strong group-specific genetic drift. There was no evidence for a recent ancestral component between the Irish Traveller and Roma populations. In addition, we formally tested evidence of admixture with f 3 statistics in the form of f 3 Irish Traveller; Settled Irish, Roma. A The first and second components from principal component analysis using gcta The estimates of clusters Traveller 1, 2 , and 3 range from 0.
Generally, however, these results suggest that the general Irish Traveller population does not have a very recent source, i. To inform on whether lineage-specific drift is influencing the observed genetic distances between the Irish Travellers, the settled Irish and other neighbouring populations, we performed outgroup f 3 analysis, using HGDP Yorubans as the outgroup. Such analysis can inform on whether PCA group B and Traveller 4 do indeed represent an older Irish Traveller group, or a sub-group that has experienced more intense drift.
We note however that f 3 statistics may not be sensitive enough to detect differences from settled Irish to Traveller PCA groups A and B should the difference between A and B be a relatively limited number of generations. A key question in the history of the Travellers is the period of time for which the population has been isolated from the settled Irish.
The method also estimates the harmonic mean N e for the two populations over the last years. The Irish Traveller estimate , std. However, the isolation of the Irish Travellers will artificially increase the F st value and consequently inflate the T F divergence estimate.
We therefore estimated the divergence time with a different IBD-based method; as such an approach can accommodate genetic drift. Specifically, a pair of Travellers share, on average, 5. These sharing patterns are not due to familial sharing, as we have previously removed individuals with close kinship see Supplementary Methods 1.
Sharing between settled and Traveller Irish was of similar extent to that within the settled group Fig. We used the number and lengths of segments shared within settled, within Travellers, and between the groups to estimate the demographic history of those populations, and in particular, the split time between these two groups. A The number and lengths of shared segments within Settled Irish, within Traveller Irish, and between the groups. Left panel: The mean segment length; middle panel: the mean number of shared segments; right panel: the mean total sequence length in cM shared between each pair of individuals.
The format of the figure is as in A. Briefly, we used the method developed in Palamara et al. We assumed a demographic model for the two populations Fig.
After this split, the settled Irish continued the exponential expansion, whilst the Irish Travellers experienced an exponential population contraction. We then computed the expected proportion of the genome found in shared segments of different length intervals using the theory of ref. A The model used for demographic inference. The two populations were one ancestral population, with size N e , T G generations ago. At this point the ancestral population started to grow exponentially until T S generations ago, where the ancestral Traveller and settled populations split from each other, with N S,T being the initial starting population size of the Traveller population.
The settled population experienced continued exponential growth until the present, with a population size of N C,S. The Traveller population experienced a period of exponential contraction until the present, with a population of N C,T. The total genome size and the sum of segment lengths were computed in cM. Left: sharing between pairs of settled Irish; middle: sharing between pairs of one settled and one Traveller individuals; right: sharing between pairs of Traveller Irish.
On the 1st of March , after 25 years of campaigning, Irish Travellers were recognised as an ethnic minority group by the Irish government.
Irish Travellers are indigenous Irish people, but are a distinctive group within the general population, and ethnically different due to a shared history, traditions, culture and language, among many other elements.
Ethnic recognition should in theory help Travellers to protect their culture and traditions, and provide extra supports in the areas including education, accommodation and health.
But the Travelling Community continue to face discrimination in many aspects of life including accessing employment, healthcare, housing and education. So far little has changed but the Travelling Community are keeping pressure on the government to improve the lives of Irish Travellers in Ireland. Traditionally, tin-smithing was widely practised among Travellers, who could hand craft many different kinds of pieces in tin or copper.
Mugs, buckets, coal scuttles and churns are only a small selection of the various items that a Traveller could make. Travellers also took up seasonal work for farmers, such as fruit and potato picking. This independent spirit is a strength and source of pride by many people in the community and is carried on to this day in the form of market stalls, gardening businesses, online selling and revamping furniture, to give only a few examples.
The pocket would hold money and important items for the family. The flap on the front would be highly decorated with hand-stitching, buttons, beads and other trinkets which were exchanged or gifted between other Traveller women.
Many Traveller women still enjoy personalising their clothing and accessories, even if they no longer make the beady pockets. The Travelling Community also have a long tradition of playing music. Uillean pipers Felix and Johnny Doran influenced pipers across the globe on the Irish traditional music scene.
Paddy Keenan is another example of this tradition. John Doherty and his family also regularly performed around Donegal, playing a unique blend of fiddle tunes. Finbar Furey also comes from a Traveller family of musicians. Travellers are usually very family-orientated and often religious. Traveller headstones are often very elaborate to demonstrate how much the person was loved by their family.
Travellers may go on religious pilgrimages including Croagh Patrick , the Camino or to visit Knock Shrine to express their faith. There are many challenges faced by Irish Travellers.
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Casey Egan. Jul 10,
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