Genetic studies on Croats
In the Bronze Age happened symbiosis between Proto-Indo-Europeans of Kurgan culture and autochthonous populations, leading to the formation among others also of Proto-Illyrians.
[4][5] They belonged to the Middle Copper Age Lasinja culture, and autosomally 70% of them were not in close kinship implying "a community composed of many family groups".
[8] Between 2018 and 2022 studies analyzed many samples related to the Cetina culture, Proto-Illyrians and specific Illyrian tribes (Iapydes and Liburni), finding that their paternal lineage almost exclusively belonged to the J2b-L283 haplogroup.
[16] In Croatia the highest frequency is observed in Dalmatia, peaking in cities of Split (50.48%), Dubrovnik (53%) and Zadar (60%),[23][19] as well southern Adriatic islands of Vis (44.6%),[23] Brač and Korčula (~55%), and Hvar (52.88-65%).
[23] The frequency is lowest in the town of Varaždin (18%) in northwestern Croatia,[19] in the western mountainous Žumberak region (18.2%),[23] and in the middle-northern islands of Cres (3%), Dugi otok (11.4%), Ugljan (24.6%) and Krk (27%).
[16][17] Based on 8 STR marker genetic distances closest are populations of near countries, but also depending on method, Ukraine, Belarus, Poland and Russia.
However, in comparison to older research which argued a prehistoric autochthonous origin of the contemporary haplogroup I2 in Croatia and the Balkans,[nb 1] Battaglia et al. (2009) already observed highest variance of the haplogroup in Ukraine, and Zupan et al. (2013) noted that it suggests it arrived with Slavic migration from the homeland which was in present-day Ukraine.
[31] Utevska calculated that the STR cluster divergence and its secondary expansion from the middle reaches of the Dnieper river or from Eastern Carpathians towards the Balkan peninsula happened approximately 2,860 ± 730 years ago, relating it to the times before Slavs, but much after the decline of the Tripolye culture.
[31] However, STR-based calculations give overestimated dates,[32][33] and more specifically, the cluster is represented by a single SNP, I-PH908, known as I2a1a2b1a1a1c in ISOGG phylogenetic tree (2019), and according to YFull YTree it formed and had TMRCA approximately 1,850-1,700 YBP.
[18] The highest local frequency of R1a1a1-M17 was observed in the Croats from Varaždin (38%) and Osijek (26-39%),[17][19] Žumberak (34.1),[23] and in the middle-northern islands of Dugi Otok (34.1%), Krk (37%), Pašman (38%) and Cres (56.6%),[14][23] being similar to the values of the other Slavs, like Slovenes, Czechs and Slovaks.
The frequency is lower in Šokci from eastern Croatia (16%),[20][21] in the city of Dubrovnik (13.4%) and Split (19%) in Dalmatia, as well on the southern islands of Hvar (8-10.58%) and Vis (17%).
[23] Based on 8 STR marker genetic distances closest are populations of near countries, but also depending on method, Belarus, Slovakia, Poland and Russia.
[38] The highest frequency of the haplogroup Haplogroup R1b (7.9%-9.1%), which in Croatia is divided into several subclades (mainly R-L23 and its subclade R-U152), has in northern (10.9%) and central (11.8%) region of Croatia,[18] while locally in the Croats from the island of Krk (16.2%) and Dugi Otok (25%),[14][23] and Žumberak (11.3%),[23] while in the southern islands, city of Dubrovnik (3.9%) and in Bosnian Croats it is almost absent (1-6%),[14][17][23][19] or like in Osijek it was not found.
[17] E-V13 it's typical of the populations of south-eastern Europe, peaking among Kosovo Albanians (44%), and is also high among the Macedonians, Greeks, Romanians, Bulgarians and Serbs.
[14][23] The haplogroup E and J are related to post-LGM, Neolithic migration of a population from Anatolia who brought with them domestication of wild animals and plants.
[15] The northern and the western parts of that sea were steppes and plains, while the modern Croatian islands (rich in Paleolithic archeological sites) were hills and mountains.
[15][17] The region had a specific role in the structuring of European, and particularly among Slavic, paternal genetic heritage, characterized by the predominance of R1a and I, and scarcity of E lineages.
It is a national reference DNA database of 17 loci system which acquired Y-STR haplotypes were predicted in estimated (over 90% probability) Y-SNP haplogroups.
[1] Preliminary results from 2016 mtDNA study, which will approximately include 30 samples from Neolithic and 5 samples from Early to Late Bronze Age, on 5 ancient Croatian petrous bones (3 Neolithic Cardial Impresso from Zemunica Cave near Bisko, 1 Middle Neolithic Danilo culture from Zidana Cave near Staničići Žumberački, 1 Mid/Late Bronze Age from Jazinka Cave near Nečven) indicated mtDNA haplogroups K2 and K1b1a, H1e/H41, H1b for Neolithic samples similar to Early European Farmers (EEFs) and modern Sardinians and Southern Europeans, while haplogroup HV or H4 for Bronze Age sample similar to modern day Croatian and Balkan population, but without clear evidence for connection with the Indo-European migration.
[8] The 2011 mtDNA study on 27 early medieval skeletal remains in Naklice near Omiš in Southern Dalmatia showed that 67% belonged to haplogroup H, 18% to J, 11% to U5, and 4% to HV.
[51] The elevated frequency of subhaplogroup H1b in Mljet (30.9%), otherwise rare in other studies, is a typical example of a founder effect – migration from the nearest coastal region and micro-evolutionary expansion in the island.
[51] Other mtDNA haplogroup with notable local peaks are: HV subclades with low frequencies in the mainland and coast (0.4-2.1%) but average (4.1-4.6) in islands, and high in Dubrovnik (7.7%)[51] and Brač (10.5%).
[55] Haplogroup N1a in Cres (9.24%) is the northernmost finding till now of this branch in Europe, and haplotypes indicate a relatively recent founder effect.
[57] Haplogroup X ranges 0.63-3.17%, mainly belonging to subclade X2 > X2b,[56] and recent research of Cres and Rab possibly found a "new, island-specific" X3 lineage which "formed within the Croatian population".
[56] On the example of population of the island of Krk, the high-resolution mtDNA analysis showed evidence that settlements Omišalj, Vrbnik, and Dobrinj are related in a joint cluster of early Slavic settlements, while Poljica and Dubašnica regions a separate cluster founded by Slavic and Vlachs or Morlachs migrants from the Velebit hinterland who arrived in the 15th century.
[51] In the 2004 mtDNA analysis, one cluster was formed by populations from islands Hvar, Krk and Brač, and second cluster included Croatian mainland and Croatian coast, while the island of Korčula was distinguished due to exceptionally high frequency of haplogroup H.[55] In the 2009 mtDNA interpopulation PCA analysis of sub-haplogroups, insular populations from Krk, Ugljan, Korčula, Brač, Hvar were clustered together implying to have close maternal lineages, with Vis close to them, but Rab (U4, H6, J1c) and especially Cres (prevalence U2, W, N1a) had separate outlying positions from both the cluster and each other, and confirmed "that genetic drift, especially founder effect, has played significant role in shaping genetic composition of the isolated population of the island of Cres".
As Slovenian population does not form Southeast Europe cluster it is considered a possible input from different migration waves of Slavs in the Middle Ages.
[64] The 2022 autosomal STR marker study on 2877 unrelated individuals from mainland (cities Zagreb, Pazin, Delnice, Zabok and Donji Miholjac, and region of Baranja) and insular (Krk, Cres, three North Dalmatian islands Ugljan-Pašman-Dugi Otok, Brač, Hvar, Korčula and Vis) subpopulations found higher genetic differentiation (0.005) compared to Southeastern Europe (0.002) indicating "a certain degree of genetic isolation, most likely due to the influence of endogamy within rural island populations".
There are visible four main clusters within sampled Croats, first including Mainland-Brač and Krk-North Dalmatian islands, second Hvar-Korčula, third Cres, and fourth Vis, the latter two having highest distances from the others.
