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BMC Evolutionary Biology

BioMed Central

Open Access

Research article

Mitochondrial DNA structure in the Arabian Peninsula
Khaled K Abu-Amero1, José M Larruga2, Vicente M Cabrera2 and
Ana M González*2
Address: 1Mitochondrial Research Laboratory, Department of Genetics, King Faisal Specialist Hospital and Research Center, Riyadh, Saudi Arabia
and 2Department of Genetics, Faculty of Biology, University of La Laguna, Tenerife 38271, Spain
Email: Khaled K Abu-Amero - abuamero@gmail.com; José M Larruga - jlarruga@ull.es; Vicente M Cabrera - vcabrera@ull.es;
Ana M González* - amglez@ull.es
* Corresponding author

Published: 12 February 2008
BMC Evolutionary Biology 2008, 8:45

doi:10.1186/1471-2148-8-45

Received: 17 September 2007
Accepted: 12 February 2008

This article is available from: http://www.biomedcentral.com/1471-2148/8/45
© 2008 Abu-Amero et al; licensee BioMed Central Ltd.
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0),
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract
Background: Two potential migratory routes followed by modern humans to colonize Eurasia
from Africa have been proposed. These are the two natural passageways that connect both
continents: the northern route through the Sinai Peninsula and the southern route across the Bab
al Mandab strait. Recent archaeological and genetic evidence have favored a unique southern
coastal route. Under this scenario, the study of the population genetic structure of the Arabian
Peninsula, the first step out of Africa, to search for primary genetic links between Africa and
Eurasia, is crucial. The haploid and maternally inherited mitochondrial DNA (mtDNA) molecule has
been the most used genetic marker to identify and to relate lineages with clear geographic origins,
as the African Ls and the Eurasian M and N that have a common root with the Africans L3.
Results: To assess the role of the Arabian Peninsula in the southern route, we genetically analyzed
553 Saudi Arabs using partial (546) and complete mtDNA (7) sequencing, and compared the
lineages obtained with those present in Africa, the Near East, central, east and southeast Asia and
Australasia. The results showed that the Arabian Peninsula has received substantial gene flow from
Africa (20%), detected by the presence of L, M1 and U6 lineages; that an 18% of the Arabian
Peninsula lineages have a clear eastern provenance, mainly represented by U lineages; but also by
Indian M lineages and rare M links with Central Asia, Indonesia and even Australia. However, the
bulk (62%) of the Arabian lineages has a Northern source.
Conclusion: Although there is evidence of Neolithic and more recent expansions in the Arabian
Peninsula, mainly detected by (preHV)1 and J1b lineages, the lack of primitive autochthonous M and
N sequences, suggests that this area has been more a receptor of human migrations, including
historic ones, from Africa, India, Indonesia and even Australia, than a demographic expansion
center along the proposed southern coastal route.

Background
The hypothesis that modern humans originated in Africa
and later migrated out to Eurasia replacing there archaic
humans [1,2] has continued to gain support from genetic

contributions [3-6]. Anthropologically, the most ancient
presence of modern humans out of Africa has been documented in the Levant about 95–125 kya [7,8], and in Australia about 50–70 kya [9]. Based on archaeological [10]
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and classic genetic studies [11,12] two dispersals from
Africa were proposed: A northern route that reached western and central Asia through the Near East, and a Southern
route that, coasting Asia, reached Australia. However, ages
for these dispersals were very tentative. The first phylogeographic analysis using complete mtDNA genomic
sequences dated the out of Africa migrations around of
55–70 kya, when two branches, named M and N, of the
African macrohaplogroup L3 radiation supposedly began
the Eurasian colonization [5,6]. A more recent analysis,
based on a greater number of sequences, pushed back the
lower bound of the out-of-Africa migration, signed by the
L3 radiation, to around 85 kya [13]. This date is no so far
from the above commented presence of modern humans
in the Levant about 100–125 kya. Interestingly, this
migration is also in frame with the putative presence of
modern humans in Eritrean coasts [14], and corresponds
with an interglacial period (OIS 5), when African faunas
expanded to the Levant [15]. After that, it seems that, at
least in the Levant, there was a long period of population
bottleneck, as there is no modern human evidence in the
area until 50 kyr later, again in a relatively warm period
(OIS 3). This contraction phase might be reflected in the
basal roots of M and N lineages by the accumulation of 4
and 5 mutations before their next radiation around 60 kya
[13].

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recent Asian or African origins. Although a newly defined
clade L6 in Yemenis, with no close matches in the extant
African populations, could suggest an ancient migration
from Africa to Yemen [30], the lack of N and/or M autochthonous lineages left the southern route without
genetic support. It could be that unfavorable climatic conditions forced a fast migration through Arabia without
leaving a permanent track, but it is also possible that sample sizes have been insufficient to detect ancient residual
lineages in the present day Arab populations. To deal with
this last possibility we have enlarged our previous sample
of 120 Saudi Arabs [31] to 553, covering the main regions
of this country (Figure 1). In this sample we sequenced the
non-coding HVSI and HVSII mtDNA regions and unequivocally assorted the obtained haplotypes into haplogroups analyzing diagnostic coding region positions by
restriction fragment length polymorphisms (RFLP) or
fragment sequencing. Furthermore, when rare haplotypes
were found, we carried out genomic mtDNA sequencing
on them. In addition, the regional subdivision of the
Saudi samples and the analysis of the recently published
mtDNA data for Yemen [30] and for Yemen, Qatar, UAE
and Oman [32] allowed us to asses the population structure of the Arabian Peninsula and its relationships with
surrounding populations.

Results
Paradoxically this expansion began in a glacial period
(OIS 4). At glacial stages it is supposed that aridity in the
Levant was a strong barrier to human expansions and that
an alternative southern coastal route, crossing the Bab al
Mandab strait to Arabia, could be preferred. Consequently, based on the phylogeographic distribution of M
and N mtDNA clusters, with the latter prevalent in western Eurasia and the former more frequent in southern and
eastern Asia, it was proposed that two successive migrations out of Africa occurred, being M and N the mitochondrial signals of the southern and northern routes
respectively [6]. Furthermore, the star radiation found for
the Indian and East Asian M lineages was taken as indicative of a very fast southern dispersal [6]. However, posterior studies revealed the presence of autochthonous M
and N lineages all along the southern route, from South
Asia [16-21], through Malaysia [13] and to Near Oceania
and Australia [22-26]. Accordingly, it was hypothesized
that both lineages were carried out in a unique migration
[27,28], and even more, that the southern coastal trail was
the only route, being the western Eurasian colonization
the result of an early offshoot of the southern radiation in
India [29,13]. Under these suppositions, the Arabian
Peninsula, as an obliged step between East Africa and
South Asia, has gained crucial importance, and indeed
several mtDNA studies have recently been published for
this region [30-32]. However, it seems that the bulk of the
Arab mtDNA lineages have northern Neolithic or more

A total of 365 different mtDNA haplotypes were observed
in 553 Saudi Arab sequences. 299 of them (82%) could
have been detected using only the HVSI sequence information and 66 (18%) when the HVSII information was
also taken into account. Additional analysis of diagnostic
positions allowed the unequivocal assortment of the
majority (96%) of the haplotypes into subhaplogroups
[see Additional file 1]. However, 11 haplotypes were classified at the HV/R level, 3 assigned to macrohaplogroups
L3*, M* and N* respectively, and only one was left
unclassified [see Additional file 1]. The most probable origin of these Saudi haplotypes deserves a more detailed
analysis.
Macrohaplogroup L lineages
Sub-Saharan Africa L lineages in Saudi Arabia account for
10% of the total. χ2 analyses showed that there is not significant regional differentiation in this Country. However,
there is significant heterogeneity (p < 0.001) when all the
Arabian Peninsula countries are compared. This is mainly
due to the comparatively high frequency of sub-Saharan
lineages in Yemen (38%) compared to Oman-Qatar
(16%) and to Saudi Arabia-UAE (10%). Most probably,
the higher frequencies shown in southern countries reflect
their greater proximity to Africa, separated only by the Bab
al Mandab strait. However, when attending to the relative
contribution of the different L haplogroups, Qatar, Saudi
Arabia and Yemen are highly similar for their L3 (34%),

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Figure 1
Map of the Arabian Peninsula showing the Saudi regions and Arabian countries studied
Map of the Arabian Peninsula showing the Saudi regions and Arabian countries studied.

L2 (36%) and L0 (21%) frequencies whereas in Oman
and UAE the bulk of L lineages belongs to L3 (72%). In
this enlarged sample of Saudi Arabs, representatives of all
the recently defined East African haplogroups L4 [30], L5
[33], L6 [30] and L7 [34], have been found. The only L4

Saudi haplotype belongs to the L4a1 subclade defined by
16207T/C transversion. Although it has no exact matches
its most related types are found in Ethiopia [30]. Four L5
lineages have been found in Saudi Arabia but all have the
same haplotype that belongs to the L5a1 subclade defined

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in the HVSI region by the 16355–16362 motif [30]. It has
matches in Egypt and Ethiopia. L6 was found the most
abundant clade in Yemen [30]. It has been now detected
in Saudi Arabia but only once. This haplotype (1604816223-16224-16243-16278-16311) differs from all the
previous L6 lineages by the presence of mutation 16243.
In addition it lacks the 16362 transition that is carried by
all L6 lineages from Yemen but has the ancestral 16048
mutation only absent in one Yemeni lineage [30]. This
Saudi type adds L6 variability to Arabia, because until
now L6 was only represented by a very abundant and a
rare haplotype in Yemen. Attending to the most probable
geographic origin of the sub-Saharan Africa lineages in
Saudi Arabia, 33 (61%) have matches with East Africa, 7
(13%) with Central or West Africa whereas the rest 14
(26%) have not yet been found in Africa. Nevertheless,
half of them belong to haplogroups with Western Africa
origin and the other half to haplogroups with eastern
Africa adscription [35,30]. It is supposed that the bulk of
these African lineages reached the area as consequence of
slave trade, but more ancient historic contacts with northeast Africa are also well documented [36,30,31].
Macrohaplogroup M lineages
M lineages in Saudi Arabia account for 7% of the total.
Half of them belong to the M1 African clade. There is no
significant heterogeneity within Saudi Arabia regions nor
among Arabian Peninsula countries for the total M frequency. However, when we compared the frequency of
the African clade M1 against that of the other M clades of
Asiatic provenance, it was significantly greater in western
Arabian Peninsula regions than in the East (χ2 = 12.53 d.f.
= 4 p < 0'05).
Inclusion of rare Saudi and other published African M1 sequences
into the M1 genomic phylogenetic tree
Recent phylogenetic and phylogeographic analysis of this
haplogroup [30,37,38] have suggested that the M1a1 subclade (following the nomenclature of Olivieri et al. [37]),
is particularly abundant and diverse in Ethiopia and M1b
in northwest Africa and the European and African Mediterranean areas. Other M1a subclades have a more generalized African distribution. Half of the M1 lineages in
Saudi Arabia belong to the Ethiopian M1a1 subclade and
the same proportion holds for other Arabian Peninsula
countries [30,32]. However, as a few M1 haplotypes did
not fit in the M1a1 cluster we did genome sequencing for
two of them (Figure 2). Lineage 471 resulted to be a member of the North African clade M1b, more specifically to
the M1b1a branch. As we have detected another M1b lineage in Jordan [38], it is possible that the Saudi one could
have reached Arabia from the Levant or from northwest
African areas. The second Saudi lineage (522) belongs to
a subcluster (M1a4) that is also frequent in East Africa
[37]. Recently, Tanzanian lineages have been studied by

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means of complete mtDNA sequences [39]. Three of these
sequences also fall into the M1 haplogroup. Two of them
belong to the Ethiopian M1a1 subclade (God 626 and
God 635), and the third (God637) shares the entire motif
that characterizes lineage M1a5 [37] with the exception of
transition 10694. Therefore, this mutation should define
a new subcluster M1a5a (Figure 2). The lineages found in
Tanzania further expand, southeastwards, the geographic
range of M1 in sub-Saharan Africa. Inspecting the M1 phylogeny of Olivieri et al. [37] we realized that our lineage
957 [38] has the diagnostic positions 13637, that defines
M1a3 and 6463 that defines the M1a3a branch. Therefore,
we have placed it as an M1a3a lineage with an 813 retromutation (Figure 2). It seems that, likewise L lineages, the
M1 presence in the Arabian Peninsula signals a predominant East African influence with possible minor introductions from the Levant.
Inclusion of rare Saudi Asiatic M sequences into the
macrohaplogroup M tree
The majority (12) of the 19 M lineages found in the Arabian Peninsula that do not belong to M1 [see Additional
file 1] have matches or are related to Indian clades, which
confirm previous results [30,31]. In addition, in this
expanded Saudi sample, we have found some sequences
with geographic origins far away from the studied area.
For instance, lineage 569 [see Additional file 1] has been
classified in the Eastern Asia subclade G2a1a [40] but
probably it has reached Saudi Arabia from Central Asia
where this branch is rather common and diverse [41].
Indubitably the four sequences (196, 479, 480 and 494)
are Q1 members and had to have their origin in Indonesia. In fact their most related haplotypes were found in
West New Guinea [42]. All these sequences could have
arrived to Arabia as result of recent gene flow. Particularly
documented is the preferential female Indonesian migration to Saudi Arabia as domestic workers [43]. Five undefined M lineages were genome sequenced (Figure 3). It is
confirmed that 5 of the 6 Saudi lineages analyzed have
also Indian roots. Lineage 691 falls into the Indian M33
clade because it has the diagnostic 2361 transition. In
addition, it shares 7 transitions (462, 5423, 8562, 13731,
15908, 16169, 16172) with the Indian lineage C182 [20],
which allows the definition of a new subclade M33a. Lineage 287 is a member of the Indian M36 clade because it
possesses its three diagnostic mutations (239, 7271,
15110). As it also shares 8 additional positions with the
Indian clade T135 [20], both conform an M36a branch
(Figure 3). Saudi 514 belongs to the Indian clade M30 as
it has its diagnostic motif (195A-514dCA-12007-15431).
Lineage 633 also belongs to the related Indian clade M4b
defined by transitions 511, 12007 and 16311. In addition
it shares mutation 8865 with the C51 Indian lineage [20]
that could define a new M4b2 subclade. We have classified sequence 551 as belonging to a new Indian clade M48

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195
6446
6680
12403
12950C
14110
16129
16189
16249
16311
M1
13111
M1b

813
6671

466
4936
8868

12346

15247g

16359

16185
M1b1
200
11671
M1b1a
4336

M1a1

M1a

13637
M1a3
6473
M1a3a
16223

3705

3513
8607

13215

M1a4

14323

199

14515

709

15770

(1781-2025)
(2053-2559)
(15720-15841)
16190d

471

303ii

150

530

303i

311i

513

813

6944

489

514dCA

1117

10873

9055

10322

11176

12403

43
Oli

183

10841

11024

13681

16182C

10881g

14696

16183C

16183C

12561

16129

16320

16249

16182C

30
Oli

957
Goz

16183C

626
God

14110
16129

635
God

13722

(1781-2025)

15799

(2053-2559)

16129
M1a5

8557

303i

(14685-15162)
489
2963
9379C

10694

M1a5a

40
Oli

14110

522

15770A

637
God

Figure 2
Phylogenetic tree based on complete M1 sequences
Phylogenetic tree based on complete M1 sequences. Numbers along links refer to nucleotide positions. A, C, G indicate transversions; "d" deletions and "i" insertions. Recurrent mutations are underlined. Regions not analyzed are in parenthesis. Star differs from rCRS [62, 63] at positions: 73, 263, 303i, 311i, 489, 750, 1438, 2706, 4769, 7028, 8701, 8860, 9540, 10398,
10873, 10400, 11719, 12705, 14766, 14783, 15043, 15301, 15326, 16223 and 16519. GenBank accession numbers of the subjects retrieved from the literature are: 43 Oli (EF060354), 30 Oli (EF060341) and 40 Oli (EF060351) from Olivieri et al. [37];
626 God (EF184626), 635 God EF184635 and 637 God (EF184637) from Gonder et al. [39]; and 957 Goz (DQ779926) from
González et al. [38].

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16519
2361

239

568i3C

M33

7271

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M42’M10

709

462
5423
8562
13731
15908
16169

15110

3168i

M36

4140

8251

7250

8793

514dCA
6320
6917
12346

16172

M33a

Q’M29

8856

12771

10646

16287
16356

12549
13152

150

14302

14502

9156

(1861-2025) 10166
(2053-2559) 16278

16193

15040

M42a

M36a

15071

5563

7406
7407

(7850-7880)

T135
(15720-15841) Sun
(4720-4750)

8593

16080

(9290-9362)

16256

(11960-12020)

16303T

13151
(14685-15162)
15238
15514
16086

287

15218
16311

M10
200
8919
12360
15218
16066
16320

ON96
Tan

204
207

211

2880 (1781-2025)
8143

5124A

3783

150
1462T

152

6104

252

709

M48

6020 (2053-2559)

303i

C182 (1781-2025) 9685
Sun (2053-2059) 16144

151

M42

14203

(5190-5279)

5460
10750
16192

4508

152

3010
1719 234

8793 13500
16311
1598

8251
9410
14527
16519

M42a1
10786

6554

464
513
1048
4230

4117
5843
8790
12940
16129
16241

10245

Q

15067

5460

16362

Q1/Q2
89

12279
8155
7711
12792 (10975-11486)
13065
14687
14040
15859
15848 16189

8964

M29

14025

4050

16144

5263

16148

9582

16265C

12127

16092

16275

16111
16293

551

R58
Sun

152

16148 4216
6962
195
311i

6374

16468

64

345

146

5447

154

8808

182

14953

514dCA

15884

92

M28

544

15896

146

94
204
12172

568i

16111A

M28b
2135
2280
3808

3547
4092
4604
6734

16311

195A

M4

6794

514dCA

11101

M14

195
6281

12007

M4’30

569

201
Abu

511

15865
16249

15431

M4b
8865

M34

241

6367

M30
(1781-2025)
207

372i

(2053-2559)
239
3866
7406 514dCA (1781-2025)
(5230-5280)
11149 3398 (2053-2559)
6710
11969 8839
8559
(9300-9362)
16051 12429 11902
(11870-12020)
16250
C51 (14685-15162)
13174
16256
16145
C56 Sun
16356
Sun
16360

633

514

8279d9

16343

5772

12366

Q1

10595

12715

5951

13452

10876

14783

M29a

7681
16223

11110

16137
16294

45
VHP

16242
16519

691

8296
9956

DQ07
Mer

12952

12507

13020

92

310

12373

Q1a

13754

13934
15498 16291 13980
16362 16318T 14182A

Q1a2 DQ99 15908
AY85 Mer 16051
Ing
16243
16245
16270A

Au38
Hud

Figure 3
Phylogenetic tree based on complete M sequences
Phylogenetic tree based on complete M sequences. Numbers along links refer to nucleotide positions. A, C, T indicate
transversions; "d" deletions and "i" insertions. Recurrent mutations are underlined. Regions not analyzed are in parenthesis.
Star differs from rCRS [62, 63] at positions: 73, 263, 303i, 311i, 489, 750, 1438, 2706, 4769, 7028, 8701, 8860, 9540, 10398,
10873, 10400, 11719, 12705, 14766, 14783, 15043, 15301, 15326, 16223 and 16519. GenBank accession numbers of the subjects retrieved from the literature are: C182 Sun (AY922276), T135 Sun (AY922287), R58 Sun (AY922299), C56 Sun
(AY922274), and C51 Sun (AY922261) from Sun et al. [20]; ON96 Tan (AP008599) from Tanaka et al. [40]; 45 VHP
(DQ404445) from van Holst Pellekaan et al. [25]; DQ07 Mer (DQ137407), DQ99 Mer (DQ137399) from Merriwether et al.
[24]; AY85 Ing (AY289085) from Ingman and Gyllensten [22]; Au38 Hud (EF495222) from Hudjashov et al. [26]; and 201 Abu
(DQ904234) from Abu-Amero et al. [31].

defined by a four transitions motif (1598-5460-1075016192) which is shared with the M Indian lineage R58
(Figure 3). Australian clade M42 [44] and New Britain
M29 clade [24] also have 1598 transition as a basal mutation. However, they are respectively more related to the
East Asia clade M10 [40] and to the Melanesian Q clade
[27], as their additionally shared basal mutations are less
recurrent than transition1598 [45]. All these Indian M
sequences have been found in Arabia as isolated lineages
that belong to clusters with deep roots and high diversity
in India. Therefore, its presence in Arabia is better
explained by recent backflow from India than by suppos-

ing that these lineages are footsteps of an M ancestral
migration across Arabia.
The Saudi sequence 201 deserves special mention (Figure
3). It was previously tentatively related to the Indian M34
clade because both share the 3010 transition. However, it
was stated that due to the high recurrence of 3010 most
probably the 201 sequence would belong to a yet undefined clade [31]. The recent study of new Australian lineages [26] has allowed us to find out an interesting link
between their Australian M14 lineage and our Saudi 201
sequence (Figure 3). The authors related M14 to the Melanesian clade M28 [24] because both share the

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1719–16148 motif [26]. We think that the alternative
motif shared with the Saudi lineage, 234-4216-6962, (Figure 3) is stronger, as 1719 and 16148 transitions are more
recurrent than 234, 4216 and 6962 [45]. Therefore, we
think that the last three mutations defined the true root of
the Australian M14 clade and relate it to a Saudi Arab
sequence.
Macrohaplogroup N lineages
All the main non R West Eurasian haplogroups that
directly spread from the root of macrohaplogroup N
(N1a, N1b, N1c, I, W, X) were present in Saudi Arabia
albeit in low frequencies [see Additional file 2]. Summing
up, their total frequency only represents 12% of the Saudi
pool. There is no heterogeneity among Saudi regions for
the joint distribution of these haplogrups, which is in contrast with the high differentiation observed (χ2 = 13.9; d.f.
3; p < 0.01) when all the Arabian Peninsula countries were
compared. However, this is mainly due to the high frequency in UAE of unclassified N* lineages [32]. The three
N1 subgroups have similar frequencies (2.4%) in Saudi
Arabia [see Additional file 2], but haplotypic diversity (h)
reach different levels being comparatively high for N1b
(0.89) or N1a (0.83) and lower for N1c (0.63). N1a is also
very diverse (0.89) in Yemen [30] but there are no haplotypic matches between both Arabian countries, and only
one (16147G-16172-16223-16248-16355) of the 7 Saudi
haplotypes has an exact match in Ethiopia. The high diversity of N1a in the Arabian Peninsula, Ethiopia and Egypt
raises the possibility that this area was a secondary center
of expansion for this haplogroup. However, the highest
diversity for N1b and N1c are in Turkey, and Kurds and
Iranians, respectively [see Additional file 3]. Only haplogroup N1c shows significant (χ2 = 12.8; d.f. 3; p < 0.01)
regional distribution in Saudi being the highest frequencies in the Northern region [see Additional file 2]. Haplogroup I has been only detected in Central and
Southeastern regions in Saudi Arabia and in all Arabian
Peninsula countries with the exception of UAE [32]. Haplogroup W has not been found in the western Saudi region
nor in the Southern Arabian Yemen and Oman countries
[30,32]. Finally, haplogroup X is present in all the Saudi
regions and in all Arabian countries excepting Oman
[30,32]. Two geographically well differentiated X
branches can be distinguished by HVSII positions [46].
The North African specific subclade X1 was defined by the
146 transition and the Eurasian specific subclade X2 by
the 195 transition. As it was already found in Yemen [30],
all the X haplotypes found in Saudi Arabia have the 195
transition, falling within the Eurasian branch, which discards East African introductions. Curiously, only the basic
haplotype (16189-16223-16278) has matches with other
regions.

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Macrohaplogroup R lineages
Macrohaplogroup R is the main branch of N and their
major subclades (H, J-T, K-U) embraced the majority of
the West Eurasian mtDNA lineages. In Saudi Arabia R
derivates represent a (70.5 ± 2.4) % of the total having a
homogeneous regional distribution. This contrasts with
the significant heterogeneity (χ2 = 46.1; d.f. 4; p < 0.001)
found for the whole Arabian Peninsula, although it is due
to the low frequency of R in Yemen (46.2%). The Western
Asia haplogroup H is the most abundant haplogroup in
Europe and the Near East [47]. However in the Arabian
Peninsula its mean frequency (9.4 ± 1.1) is moderate,
reaching its highest value in Oman (13.3%) and its lowest, again, in Yemen (7.2%). Within Saudi Arabia, the
highest frequencies are in the Northern and Central
regions (9.3%) and the lowest in the West region (2.8%),
being CRS, H2a1 and H6 the most abundant subclades
which confirm other authors results [48]. Haplogroup T
shows regional heterogeneity in Saudi Arabia (χ2 = 10.4;
d.f. 3; p < 0.05) and has significantly lower frequencies in
Southern Yemen and Oman countries (χ2 = 5.8; p < 0.05).
Furthermore, whereas subclade T3 is the most abundant
in the Saudi Central region, subclades T1 and T5 are so in
Northern and Western regions. Haplogroup U comprises
numerous branches (U1 to U9 and K) that have different
geographic distributions [47,16,17,49]. In Saudi Arabia
all of them have representatives albeit in minor frequencies, K (4%) and U3 (2.3%) being the most abundant
clades. There is no geographical heterogeneity for the total
U distribution in Saudi Arabia. Nevertheless, it is significantly different among the Arabian Peninsula countries
(χ2 = 12.0; d.f. 4; p < 0.05), with Southern countries showing higher frequencies than the others [see Additional file
3]. Analysis of specific haplogroups reveals some interesting geographic distributions in the Arabian Peninsula.
The European clade U2e and the rare clade U9 (χ2 = 10.5;
d.f. 4; p < 0.05) could have reached the Arabian Peninsula
from northern areas. On the contrary, the Indian clade U2
(χ2 = 34.5; d.f. 4; p < 0.001), U3, U4, U7 (χ2 = 11.7; d.f. 4;
p < 0.05) and K (χ2 = 10.5; d.f. 4; p < 0.05), most probably
came from the East. Finally, the North African clade U6,
had a Western provenance. Haplogroup (preHV)1 was
phylogenetically and phylogeographically studied in
detail previously [31]. However, this enlarged Saudi sample has allowed a regional analysis in Saudi Arabia. An
heterogeneity test showed that (preHV)1 is significantly
(χ2 = 8.5; d.f. 3; p < 0.05) more abundant in Northern
(18.6%) and Central (21.8%) regions, and has particularly low frequency in the West region (8.3%). Extending
the analysis to the whole Arabian Peninsula the heterogeneity grows considerably (χ2 = 30.9; d.f. 4; p < 0.001). This
is mainly due to the comparatively lower frequencies in
Yemen, Qatar and UAE [see Additional file 3]. Most probably, this haplogroup reached Arabia from the North [31],
extending its geographic range to the South using mainly

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internal instead of coastal routes. As a whole, haplogroup
J reaches its highest frequency in Saudi Arabia [31], where
its regional distribution is also significantly heterogeneous (χ2 = 15.0; d.f. 3; p < 0.01), but opposite to that found
for (preHV)1. For the J, the West (37.5%) and Southeast
(25.7%) regions have higher frequencies than the Central
(17.6%) and North (16.3%) regions. Heterogeneity in the
whole Peninsula is also significant (χ2 = 16.5; d.f. 4; p <
0.01) being Saudi Arabia (21%) and Qatar (17.8%) the
two countries with the highest J frequencies. However, the
subclade distribution is different in each country. Subclade J1b is the main contributor (9.4%) in Saudi Arabia
while other J subclades account for 14.5% in Qatar [see
Additional file 3]. With the Qatar exception, J1b is the
most frequent subclade in the Arabian Peninsula [see

Additional file 3]. So for, it deserves more detailed phylogenetic and phylogeographic studies.
Phylogeny of haplogroup J1b
We have used 23 haplogroup J complete sequences to
construct a refined J1b phylogeny. As a subclade of J1, J1b
is characterized by transition 462 and 3010 [50]. In addition, J1b is defined by transition 8269 in the coding
region and by the HVSI motif, 16145-16222-16261 (Figure 4). Transitions 5460 and 13879 are now diagnostic of
the J1b1 subclade, previously named J1b [47,18]. In addition, the 242-2158-12007 motif defines a J1b1a branch.
Furthermore, sequences carrying transitions 8557 and
16172 cluster now into the J1b1a1 clade formerly named
J1b1 [47,18]. Finally, transition 15067 defines an addi-

462
3010
J1
8269
16145
16222
16261
J1b

5460

1709
4232
8460

13879
J1b1
242
2158
12007

271
8494
13656

15530

J1b1a
3543

16274

8269

16519

12346

185

9T

4679

R80
Pal

14016

1462

10

234
Cob

498
Her

7299

238
Cob

231
Cob

8557
16172
J1b1a1

235
Cob
B30
Pal

1733
J1b2

15788

6911

16224

12311

(16024-576)(16321-576) 15467

501
Her

L21
Ros

232
Cob

15067
J1b1a1b

7
Est
5298

2157

237
Cob

5705

236
Cob

5501
6902

491
Jus

16519

303i

15735

4991

488
489
490
492
Jus

(16024-576)

5463

303i
6719

14927

87
MM

11778

15941

(16024-576) 6345

14180

264

233
Cob

8281i

(16321-576) 8286
L170 12007
16274

Ros
311i

2158

16186

16247

181
Fin

180
Fin

Figure 4
Phylogenetic tree based on complete J1b sequences
Phylogenetic tree based on complete J1b sequences. Numbers along links refer to nucleotide positions. T indicates
transversion and "i" insertions. Recurrent mutations are underlined. Regions not analyzed are in parenthesis. Star differs from
rCRS [62, 63] at positions: 73, 263, 295, 311i, 489, 750, 1438, 2706, 4216, 4769, 7028, 8860, 10398, 11251, 11719, 12612,
13708, 14766, 15326, 15452A, 16069 and 16126. GenBank accession numbers of the subjects retrieved from the literature are:
R80 Pal (AY714033) and B30 Pal (AY714035) from Palanichamy et al. [18]; 498 Her (EF657673) and 501 Her (EF657678) from
Herrnstad et al. [64]; 238 Cob (AY495238), 231 Cob (AY495231), 234 Cob (AY495234), 235 Cob (AY495235), 232 Cob
(AY495232), 236 Cob (AY495236), 237 Cob (AY495237) and 233 Cob (AY495233) from Coble et al. [65]; L21 and L170 from
Rose et al. [66]; 181 Fin (AY339582) and 180 Fin (AY339581) from Finnilä et al. [50]; 7 Est from Esteitie et al. [67]; 87 MM
(AF381987) from Maca-Meyer et al. [6]; 488 (DQ282488), 489 (DQ282489), 490 (DQ282490), 492 (DQ282492) and 491 Jus
(DQ282491) from Just et al. [68].

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BMC Evolutionary Biology 2008, 8:45

tional J1b1a1b group (Figure 4). In order to accurately
incorporate our previously published J1b Moroccan
sequence [6] into the present phylogeny, we have resequenced all the fragments comprising any mutation
present in related branches. Only transition 8269 was
overlooked in our anterior analysis. This Moroccan
sequence shares the 1733 transition with four Hispanic
sequences defining a new J1b2 clade (Figure 4). Using
time for the most recent common ancestor (TMRCA) as
an upper bound for a cluster radiation, we estimated a
Paleolithic time of 29,040 ± 8,061 years for the entire J1b
clade and a Neolithic age of 9,175 ± 3,092 years for the
J1b1a1 subclade.
Phylogeography of haplogroup J1b
Figure 5 shows the reduced median network obtained
from 173 J1b HVSI based haplotypes, found in a search of
6665 HVSI sequences belonging to the Arabian Peninsula
and the surrounding Near East, Caucasus-Caspian, and
North and Northeast African regions [see Additional files
4 and 5]. The basic central motif (16069-16126-1614516222-16261) is the most abundant and widespread haplotype in the four areas. In Saudi Arabia this motif is particularly abundant being responsible of the relative low
variability of J1b in this country (Table 1). The radiation
of this clade widely affected the five studied areas and
extended to the European and North African countries of
the Mediterranean basin although in low frequencies.
One of the main offshoots of the J1b radiation is the
J1b1a1 subclade characterized in the HVSI region by the
16172 transition. It is widespread in the Near East, the
Caucasus, and Northern and Central Europe where its
diversity is the highest (Table 1). However it has not been
detected in the Arabian Peninsula. It seems therefore that
the first J1b radiation mainly affected southern countries
whereas secondary spreads reached northern areas probably due to better climatic conditions. At this respect it is
worth mentioning that a subsequent J1b1a1 radiation
characterized by the basic 16192 transition (J1b1a1a subclade) had a northwest European expansion being a Georgian and a Russian its only detected outsiders [51]. In
addition, several J1b expansions, as those rooted by the
16235 and the 16287 transitions, occurred in the Near
East; whereas others, as those represented by the 16093
and the 16136 basic transitions, were mainly confined to
the Arabian Peninsula (Figure 5). The TMRCA for the
whole J1b haplogroup based on HVSI sequences was of
19,480 ± 4,119 years, which is more in accordance with
the age of the group obtained from complete sequences
and applying the Ingman et al. [5] mutation rate (21,524
± 5,974) than with the previously cited estimation based
on that of Mishmar et al. [52]. However, in all cases this
radiation is placed in the Paleolithic. On the contrary, the
HVSI based age for J1b1a1 (10,621 ± 4,982) is closer to
that obtained following Mishmar et al. [52] (9,175 ±

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3,092) than that obtained (6,800 ± 2,292) according to
Ingman et al. [5]. For the age calculation of the Arab
16136 branch, two Yemeni Jews that shared the 1606916126-16136-16145-16221
haplotype [47] were
included. The age obtained (11,099 ± 8,381 years) is similar to that calculated for the northern J1b1a1 subclade,
pointing to a simultaneous spread of different J1b
branches in different geographic areas most probably due
to generalized mild climatic conditions.
Population based comparisons
In order to assess the degree of regional differentiation in
Saudi Arabia we performed AMOVA analyses, based on
haplogroup (p < 0.001) and haplotypic (p < 0.05) frequencies. They showed significant inter regional variability, mainly due to the heterogeneous composition of the
Central Region. Haplogroup frequency differentiation is
also found when all the Arabian Peninsula countries were
taken into account (p < 0.01). In spite of this, when the
Arabian Peninsula samples were compared with those of
surrounding African, Near East and Caucasus areas by
means of pair-wise FST distances, based on haplogroup frequencies, and their relationships graphically represented
(Figure 6), it is worth mentioning that all the Saudi samples, including a small Bedouin sample [53], closely cluster together. However, two Arabian Peninsula countries,
Yemen and UAE, showed marginal positions. The first,
due to its greater frequency of African L haplogroups, congruently approaches Egypt and Nubian, whereas the second, due to the relative scarcity of this African component
and the greater contribution of Eurasian clades (as HV,
some T subgroups, and the whole U haplogroup, excepting U6) to its mtDNA pool, is placed in close proximity to
the Near East samples (Figure 6).

Discussion
Eurasian and African influences in the Arabian Peninsula
Although until recent times the majority of the Saudi Arabia population was nomad, a moderate level of mitochondrial genetic structure has been found amongst its
different regions. This heterogeneity grew considerably
when all the Arabian Peninsula countries were included in
the AMOVA analysis. It seems that the main cause of this
diversity is the unequal influence that the different areas
received from their geographically closest neighbors. This
fact is graphically reflected in the MDS plot (Figure 6)
where all the Arabian Peninsula samples are compared
with samples from East Africa, the Near East and the Caucasus areas. The clustering of all the Saudi regions clearly
shows that, in comparison to other geographically more
distant populations, they form a rather homogenous
entity, as was previously suggested from analysis based on
classical markers [12]. The more distant positions of
Yemen, grouped with African samples, and the UAE, and
in a lesser degree the Qatar and Oman, proximity to Near

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Figure 5
Reduced median network relating J1b HVSI sequences
Reduced median network relating J1b HVSI sequences. The central motif (star) differs from rCRS at positions: 16069
16126 16145 16222 16261 for HVI control region. Numbers along links refer to nucleotide positions minus 16000: homoplasic
mutations are underlined. The broken lines are less probable links due to mutation recurrence. Size of boxes is proportional to
the number of individuals included. Codes are: Am = Armenian, Ar = Saudi Arab, Bd = Bedouin Arab, Eg = Egyptian, Ge =
Georgian, In = Iranian, Iq = Iraqi, Jo = Jordanian, Ka = Kazakhs, Ki = Kirghiz, Ku = Kurd, Mo = Moroccan Berber, NC = Caucasian, Om = Omani, Pa = Palestinian, Qa = Qatar, Sy = Syrian, Ta = Tajik, Tm = Turkmen, Tn = Tunisian, Tu = Turk, UA =
United Arab Emirates, UZ = Uzbek, Ye = Yemeni.

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Table 1: K haplotype diversity (in %) and π (× 1000) diversity for
the total J1b, J1b1a1 and J1b1a1a subhaplogroups.

haplotypes

sample

K

π

J1b

Ara-tot
Cau-tot
NE-tot
Eu-tot

15
14
29
35

81
23
56
112

19
61
52
31

3.59 ± 2.65
7.91 ± 4.98
8.67 ± 5.23
6.32 ± 4.02

J1b1a1

Ara-tot
Cau-tot
NE-tot
Eu-tot

4
4
20

0
8
10
88

50
40
23

2.50 ± 2.33
3.78 ± 3.02
3.97 ± 2.84

Ara-tot
Cau-tot
NE-tot
Eu-tot

1
7

0
1
0
41

100
17

1.59 ± 1.56

J1b1a1a

East countries, reflect their different frequencies of African
and Eurasian lineages in their respective mitochondrial
pools. Roughly, the African contribution to whole Arabian Peninsula accounts for 20% of its lineages if, in addition to all the L haplogroups, the North African M1 and
U6 clades are added. However, the western and southern
areas have received significantly stronger influences than
the rest. Particularly, Yemen has the largest contribution
of L lineages [30]. So, most probably, this area was the
entrance gate of a portion of these lineages in prehistoric
times, which participated in the building of the primitive
Arabian population. Later, received gene flows from
North Africa and the Near East, and suffered expansions

Figure 6
Graphical relationships among the studied populations
Graphical relationships among the studied populations. MDS plot based on FST haplogroup distances. Codes
are: Ce = Central Saudi Arab, Dz = Druze, Et = Ethiopian, Ke
= Kenyan, No = Northern Saudi Arab, Nu = Nubian, SE =
Southeastern Saudi Arab, Su = Sudan, We = Western Saudi
Arab. Others codes as in Figure 5.

and retractions in humid or arid climatic periods. These
fluctuations are also reflected in the frequent loss of diversity for several African clades as the L6 in Yemen [30] or
the L5 in Saudi Arabia. However, the presence of western
Africa L lineages and the different composition of L subclades in the African pool of different countries might
reflect unequal participation of the primitive and the
recent slave trade substrates in their respective African
components.
An important group of the Arabian Peninsula lineages
(18%), comprising representatives of the majority of the
U clades, R2, and Central Asian, Indian, and Indonesian
M lineages, seem to have their origins in the East, reaching
the Arabian Peninsula through Iran where, in contrast to
the Near East, the U clades (29%) have the highest frequency instead of the H (17%) group [49]. Congruently,
this Eastern gene flow had a significantly stronger impact
in the Eastern and Southern areas of the Arabian Peninsula. However, the bulk of the Arabian N and R lineages
(62%) had a Northern source. Haplogroups (preHV)1
and J1b were the main contributors of this gene flow. Nevertheless, its present day geographic distributions in the
Arabian Peninsula are different. Whereas (preHV)1
presents significant higher frequencies in the North and
Central Saudi regions and in Oman, J1b shows its highest
frequencies in the more peripheral West and Southeast
Saudi regions. It seems that at least haplogroups H, N1c
and subclade T3 could have followed the (preHV)1 internal way of dispersion, while the T1 and T5 branches of
haplogroup T and other branches of haplogroup J followed the peripheral route of clade J1b. Attending to the
radiation ages of (preHV)1 and J1b clades and their derivate branches, striking similarities but also differences can
be observed. The first expansion of both clades in the Near
East had similar Paleolithic ages around 20,000 years ago.
However whereas the ancestral HVSI motif of the
(preHV)1 expansion was barely present in Saudi Arabia
[31], the ancestral HVSI motif of the J1b radiation had an
important incidence in that area (Figure 5) suggesting an
active role in Arabia of the first J1b spread but not for that
of (preHV)1. The succeeding most important radiations of
both clades, (preHV)1a1 and J1b1a1 had, again, similar
ages around 10,000 years that place them in Neolithic
times. Now, in both cases, there is a shortage or absence
of the ancestral motif in Arabia discarding this area as a
radiation center. However, it participated in the
(preHV)1a1 spread [31] but not in the J1b1a1 one (Figure
5). Finally, the third more abundant subclades,
(preHV)1b rooted by 16304 [31] and J1b rooted by
16136 (Figure 5) had the Arabian Peninsula as the most
probable source of expansion. Nevertheless, whereas the
J1b branch TMRCA (11,099 ± 8,381 years ago) was contemporary to that of the northern J1b1a1, the recalculated
age of the (preHV)1b branch (by adding all the new HVSI

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sequences found in the present survey to the ones previously used [31]), was of only 4,036 ± 2,211 years ago
which situates this expansion in the Bronze Age. These
results could be satisfactorily explained if we admit an
older Paleolithic implantation in Saudi Arabia of the J1b
clade that, perhaps, with some other N and L clades would
form the primitive population. Posterior (preHV)1 subclade radiations, accompanied by other clades, penetrated
from the North using internal routes and even had secondary spreads in central Arabia diluting the J1b frequencies in these areas and causing its peripheral distribution.
Genomic dissection of rare M lineages
By genomic sequencing of seven M lineages (Accession
numbers: EU370391–97), it has been demonstrated that
the majority of the rare M lineages detected in Saudi Arabia (Figure 3) have Indian roots. However, the link found
between the M Saudi 201 sequence and an M14 Australian sequence is puzzling. Although at first sight it could be
taken as a signal of the connection between the two
utmost ends of the southern route, it seems not to be the
case. First, both lineages share three basal positions and
this hypothetical link would considerably delay the arrival
age of M in comparison to that of East Asia. It would be
improbable that similar Australian links with other M lineages mainly from India were not found. Third, if the Arab
lineage had such an old implantation in the Arabian
Peninsula some detectable autochthonous radiation
should be expected. Most probably, the M42 sequence
belongs to an Australian clade and its related lineage
found in Saudi Arabia is also of Australian origin. Historical links as those invoked to explain the presence of
Indian and Indonesian sequences in the Arabian Peninsula pool should also be valid for this case. In our opinion, the camel trade between Saudi Arabia and Australia
[54] could be a probable historic cause of this link. Future
detection in Aboriginal Australians of other M42 lineages
will confirm the Australian origin of this clade and its
radiation age in that Continent. However, the link
between the East Asia M10 clade [40] and the Australian
M42 clade, if not due to convergence, seems to be more
interesting as it would confirm, once more, the rapid
expansion of macrohaplogroup M all along the Asian
coasts [6,13]. The lack of autochthonous M and N lineages in the present day Arabian Peninsula populations
confirms that this area was not a place of demographic
expansion in the dispersal out of Africa [55].

Conclusion
Although there is evidence of Neolithic and more recent
expansions in the Arabian Peninsula, mainly detected by
(preHV)1 and J1b lineages, the lack of primitive autochthonous M and N sequences, suggests that this area has
been more a receptor of human migrations, including historic ones, from Africa, India, Indonesia and even Aus-

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tralia, than a demographic expansion center along the
proposed southern coastal route.

Methods
Study population
Buccal swabs or peripheral blood were obtained from 553
(120 of them previously published in Abu-Amero et al.
[31]) maternally unrelated Saudi Arabs all whose known
ancestors were of Saudi Arabian origin. The main Saudi
Arabian geographic regions were sampled (Figure 1 and
Additional file 1). Sequence analysis was performed of
mtDNA regulatory region hypervariable segment I (HVSI)
and hypervariable segment II (HVSII) and of haplogroup
diagnostic mutations using RFLPs or partial sequencing
[see Additional file 1]. In addition, genomic mtDNA
sequencing was carried out in 7 individuals of uncertain
or interesting haplogroup adscription. For population
and phylogeographic comparison, we used 21,808 published or unpublished partial sequences from Europe
(11,174), South Asia (2,746), Caucasus (1,638), North
Africa (1,009), East Africa (888), Near East (2,001), Arabian Peninsula (1,129) and Jews (1,223), as detailed in
Additional files 4 and 5. Informed consent was obtained
from all individuals.
MtDNA sequencing
Total DNA was isolated from buccal and blood samples
using the PUREGENE DNA isolation kit from Gentra Systems (Minneapolis, USA). HVSI and HVSII segments were
PCR amplified using primers pairs L15840/H16401 and
L16340/H408, respectively, as previously described [6].
Genomic mtDNA sequences and segments including
diagnostic positions were amplified using a set of 32 separate PCRs and cycling conditions as detailed elsewhere
[6]. Successfully amplified products were sequenced for
both complementary strands using the DYEnamic™ ET
dye terminator kit (Amersham Biosciences), and samples
were run on MegaBACE 1000 (Amersham Biosciences)
according to the manufacturer protocol.
Haplotype classification
Classification into sub-haplogroups was performed using
nomenclature previously described for African [35,30,34]
and for Eurasian [47,49,40,24,20,37,31,26] sequences.
Published sequences employed for comparative genetic
analysis were re-classified into sub-clades using the same
criteria in order to permit comparisons.
Genetic analysis
Haplotype diversity was calculated as h [56] and as K
(haplotype number/sample size quotient). Only HVSI
positions from 16069 to 16385 were used for genetic
comparisons of partial sequences with other published
data. Genetic variation was apportioned within and
among geographic regions using AMOVA by means of

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BMC Evolutionary Biology 2008, 8:45

ARLEQUIN2 [57]. Four regions (North, Central, West and
South-East) were considered to assess the Saudi Arabia
genetic structure (Figure 1 and Additional file 2). For more
extended geographic comparisons the following areas
were taken into account: Arabian Peninsula (including
Saudi Arabia, Qatar, UAE, Oman, Yemen and Bedouin
Arabs), North-East Africa (including samples from Egypt,
Nubian, Sudan, Ethiopia, and Kenya), and Near East
(containing samples from Druze, Iran, Iraq, Jordan,
Kurds, Palestine, Syria and Turkey), as detailed in Additional file 3. Pairwise FST distances between populations
were calculated from haplogroup and haplotype frequencies, and their significance assessed by a nonparametric
permutation test (ARLEQUIN2). Multidimensional scaling (MDS) plots were obtained with SPSS version 13.0
(SPSS Inc., Chicago, Illinois). Phylogenetic relationships
among HVSI and genomic mtDNA sequences were established using the reduced median network algorithm [58].
In addition to our 7 genomic mtDNA sequences, 7, 12
and 23 published complete or nearly complete mtDNA
sequences were used to establish the M1 (Figure 2), M
(Figure 3) and J1b (Figure 4) phylogenies, respectively.

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Additional material
Additional File 1
HVS I and II sequences and RFLP results for the Saudi Arabs analyzed.
The data provided shows the ID, geographic localization, HVS I and II
sequence, and RFLPs for each individual analyzed.
Click here for file
[http://www.biomedcentral.com/content/supplementary/14712148-8-45-S1.xls]

Additional File 2
Haplogroup frequencies (in percentage) and sample size for the different
Saudi Arab regions. The data show the sample size and haplogroup frequencies (in percentage) for each of the different regions (central, north,
southeast, west, and miscellaneous sample) analyzed in Saudi Arab.
Click here for file
[http://www.biomedcentral.com/content/supplementary/14712148-8-45-S2.xls]

Additional File 3
Sample size and frequency (in percentage) of different groups in the populations studied, used to estimate the FST between them. The data show
the sample size, and haplogroup frequencies (in percentage) for the following studied populations: Saudi Arab, Yemen, Oman, Qatar, United
Arab Emirates, Bedouins, Iran, Iraq, Syria, Palestine, Jordan, Druze, Turkey, Kurd, Egypt, Kenya, Nubian, Sudan, and Ethiopia.
Click here for file
[http://www.biomedcentral.com/content/supplementary/14712148-8-45-S3.xls]

Time estimates
Only substitutions in the coding region were taken into
account for complete sequences, excluding insertions and
deletions. The mean number of substitutions per site
compared to the most common ancestor (ρ) of each clade
and its standard error were calculated following Morral et
al. [59] and Saillard et al. [60] respectively, and converted
into time using previously published substitution rates
[5,52]. For HVSI, the age of clusters or expansions was calculated as the mean divergence (ρ) from inferred ancestral
sequence types [59,60] and converted into time by assuming that one transition within np 16090–16365 corresponds to 20,180 years [61].

Additional File 4
Populations searched for J1b haplotypes. The table lists the populations
and geographic areas used to search for J1b haplotypes. Sample sizes and
references for each population are also indicated.
Click here for file
[http://www.biomedcentral.com/content/supplementary/14712148-8-45-S4.xls]

Additional File 5
References used in Additional file 4. References cited in Additional file 4
are detailed.
Click here for file
[http://www.biomedcentral.com/content/supplementary/14712148-8-45-S5.doc]

Accession numbers
The seven new complete mitochondrial DNA sequences
are registered under GenBank accession numbers:
EU370391–EU370397

Authors' contributions
KKAA, JML, VMC and AMG conceived and designed the
experiments and wrote the paper. KKAA and VMC performed the experiments. JML and AMG analyzed the data.
All the authors read and approved the final manuscript.

Acknowledgements
This research was supported by grant BFU2006-04490 from Ministerio de
Ciencia y Tecnología to J.M.L. We would like to thank Rebecca S. Just and
coauthors for allowing us the use of their unpublished and valuable data.

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Stringer CB, Andrews T: Genetic and fossil evidence for the origin of modern humans. Science 1988, 239:1263-1268.
Cann RL, Stoneking M, Wilson AC: Mitochondrial DNA and
human evolution. Nature 1987, 325:31-36.

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