Y-chromosome and mtDNA polymorphisms in Iraq, a crossroad of the early human dispersal and of post-Neolithic migrations

https://doi.org/10.1016/S1055-7903(03)00039-3Get rights and content

Abstract

Analyses of mtDNA and Y-chromosome variation were performed in a sample of Iraqis, a scarcely investigated population of the “Fertile Crescent.” A total of 216 mtDNAs were screened for the diagnostic RFLP markers of the main Eurasian and African haplogroups. A subset of these samples, whose HVS-I sequences were previously obtained, was also examined by high-resolution restriction analysis. The Y-chromosome variation was investigated in 139 subjects by using 17 biallelic markers and the 49a,f/Taq I system. For both uniparental systems, the large majority of the haplogroups observed in the Iraqi population are those (H, J, T, and U for the mtDNA, and J(xM172) and J-M172 for the Y chromosome) considered to have originated in the Middle East and to have later spread all over Western Eurasia. However, about 9% of the mtDNAs and 30% of the Y-chromosomes most likely represent arrivals from distant geographic regions. The different proportion of long-range genetic input observed for the mtDNA and the Y chromosome appears to indicate that events of gene flow to this area might have involved mainly males rather than females.

Introduction

Iraq is an Arabian country bordered by the Arabian gulf, Kuwait, Saudi Arabia (South), Jordan and Syria (West), Turkey (North), and Iran (East) (Fig. 1). Iraq is composed of a mountainous region in the Northeast and a vast desert in the Southwest; in between is the heart of the country, a fertile low land region irrigated by the Tigris and Euphrates rivers, corresponding to the ancient Mesopotamia. The Iraqi population, ca. 21.5 million individuals (July 1995), consists of 75–80% Arabs, 15–20% Kurds, and 5% Assyrians, Turkmen, and others. The official language is Arabic, a Semitic language belonging to the Afro-Asiatic family, but other languages are also spoken: Kurdish (Indo-European), Assyrian (Semitic), and Armenian (Indo-European).

Modern humans are likely to have been present in this area from the time of the exit from Africa around 60,000 years ago, but little information is available about the Palaeolithic period. As for Neolithic times, Iraq represents one of the most important areas for the development and diffusion of agriculture dating from 10,000 years ago onward as testified by many archaeological remains at the Shanidar and Karim Shahir sites (Rashed, 1997). In addition, this region was the source of several ancient civilizations (Sumerians, who first introduced the use of writing, Babylonians, Assyrians, and Caldeans) that profoundly affected other populations of the Middle East, Europe, and elsewhere.

In spite of the importance of this region, genetic studies on the Iraqi population are scarse, aged, and generally restricted to analyses of classical markers (Cavalli-Sforza et al., 1994 and references therein), thus not allowing a dissection of its genetic structure. Analyses of mtDNA and Y-chromosome variation have indicated the central role of the Middle Eastern area in the dispersal of human populations by revealing that it was the probable homeland of numerous mtDNA and Y-chromosome haplogroups (Macaulay et al., 1999; Quintana-Murci et al., 2001; Richards et al., 1998; Semino et al., 2000a; Torroni et al., 1998). However, while extensive studies were carried out in several populations of this region (Comas et al., 1998; Hammer et al., 2000; Nebel et al., 2001; Quintana-Murci et al., 2001; Ritte et al., 1993; Salem et al., 1996; Santachiara-Benerecetti et al., 1993), only few components of mtDNA and Y-chromosome Iraqi gene pool have been evaluated (Quintana-Murci et al., 1999b; Richards et al., 2000). Thus, to increase the knowledge of the genetic structure of that population and to better understand the relationships between the Middle East, Asia Minor, and Europe, we have investigated the extent and nature of mtDNA and Y-chromosome variation in a sample of Iraqi subjects.

Section snippets

Subjects

Blood samples were collected in Baghdad from 216 unrelated adult males (178 Arabs, 25 Assyrians, and 13 Kurds) whose origin was ascertained, at least up to four generations, by oral interview, and who were from different villages and towns along the Tigris and Euphrates rivers. Genomic DNA was extracted from buffy-coats by using standard procedures.

MtDNA analysis

A total of 216 mtDNAs were analyzed for the diagnostic RFLP markers of the most common European, Asian, and African haplogroups (Macaulay et al.,

MtDNA variation

Table 1 shows the haplogroup frequencies obtained by screening all Iraqi mtDNAs for the diagnostic RFLP markers. Their distribution is similar to that of Iran and, in general, to the Middle Eastern populations whereas it substantially differs from that observed in Arabia. Haplogroups HV, H, V, J, T, K, U, I, X, and W encompass about 78% of the Iraqi subjects. This overall frequency is in the range of the other Middle Eastern population values (75.1–80.4%) which are closer to Europe (>90%) than

Discussion

The study of the Iraqi population through the analysis of maternal and paternal markers helps to fill a gap in the picture of the Middle Eastern genetic population structure. As illustrated by the PC analysis of the mtDNA data (Fig. 5), Iraq clusters with the other Middle Eastern populations, and together with Iran, occupies a central position among Arabia, Caucasus, and Europe. The first component separates Arabia from the others, mainly from Europe and Caucasus, being the Arabia characterized

Acknowledgements

This research was supported by the Italian Ministry of the University, Progetti Ricerca Interesse Nazionale 1999 and 2002 (to A.S.S.-B. and A.T.), Progetto Finalizzato C.N.R. “Beni Culturali” (to A.S.S.-B.), as well as from Fondo d’Ateneo per la Ricerca dell’Università di Pavia (to A.S.S.-B. and A.T.). N.A.-Z. was supported by ICGBE (Trieste) and University of Pavia fellowships.

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