Abstract

Mitochondrial DNA is a small genome, 16569 base pairs in length, which is found in high quantities within mitochondria inside a typical somatic cell. Mitochondrial DNA is also unilaterally inherited via the maternal line. As such, mitochondrial DNA is inherited relatively unmolested from mother to offspring, with exception to mutational episodes, enabling the historical analysis of a population, group of populations or a species. Mitochondrial DNA analysis examines both the coding and non-coding regions for the presence or absence of single nucleotide polymorphisms. When a particular collection of polymorphisms are present, the mitochondrial DNA can be assigned to a genetic group known as a haplogroup. The identification of polymorphisms within the non-coding region (D-loop) illustrates the mitochondrial DNA haplotype. Many haplogroups are region-specific, in that they often present among populations of a geographical region, while presence of haplogroups from adjacent regions can infer adjustments to population structure via gene flow from migratory events. Afghanistan is a landlocked, Central Asian country which has held a significant strategic position throughout history as a thoroughfare for ancient trade routes and human migrations. As a consequence, Afghanistan has a vast diversity of ethnic groups. This study aimed to analyse the mitochondrial DNA genome to identify the haplogroup composition and distribution among four ethnic groups of Afghanistan; the Baluch, Hazaras, Pashtuns and Tajiks which together account for ~80% of the total Afghani population. Afghanistan is a previously unstudied population, and this study aims to determine whether the haplogroup composition has been influenced by numerous demographic events. The Baluch, Pashtun and Tajik ethnic groups believe they have ancestry from west Eurasia and the Middle East, while the Hazaras believe they are of Mongol descent and this study also aimed to identify whether the mtDNA haplogroups observed supported the belief systems of the Afghani ethnic groups and provide indications of their ancestry. The mitochondrial DNA analysis illustrates that the Hazara possess a large East Asian haplogroup contribution of 37.5%, while the Baluch, Pashtuns, and Tajiks possess a much lesser contribution; less than 14.3%. Meanwhile, the Baluch, Pashtuns and Tajiks each enjoy a large west Eurasian haplogroup contribution of at least 64.3% while the Hazaras exhibit a west Eurasian haplogroup frequency of 40%. The Hazaras have the most diverse collection of haplogroups, with only two haplogroups out of the seventeen observed overall absent from this ethnic group. The Pashtuns have the greatest HVS-I sequence diversity as no haplogroup is shared within the ethnic group. As a whole, the Afghani populations exhibit a high gene diversity (>0.98). The Hazara, Pashtun and Tajik populations are considered to be expanding populations, or have recently experienced an expansion process based upon mismatch distributions. This is supported by a star-like phylogeny in a Median-Joining network. Genetic barriers were observed when analysing Afghani HVS-I with an additional 3923 mitochondrial DNA HVS-I sequences from 62 populations; separating the Iranian Baluch population from the Afghani Baluch, also the Afghani populations from the Pakistani, Indian Bhargava, Chinese and Mongol populations. The same analysis has inferred the Afghani ethnic groups observed are share a greater affinity with west Eurasian and Central Asian populations rather than to populations of South Asia or East Asia. The haplogroup analysis indicates the Baluch, Pashtuns and Tajiks share some sort of ancestral heritage, while the Hazaras, due to their greater East Asian lineage contribution, may be descendants of a major East Asian expansion, possibly from the Genghis Khan line, and have experienced a more recent maternal gene flow. These results illustrate the impact of the historical expansions and migrations have had upon the Afghani population. 

Additional Notes

Supervisor: Dr. Maziar Ashrafian Bonab

Course: Master of Philosophy - MPhil

Date Deposited: 2017-05-17

URI/permalink: https://library.port.ac.uk/dissert/dis12892.html