Genetic studies on Sinhalese

Genetic studies on the Sinhalese is part of population genetics investigating the origins of the Sinhalese population.
All studies agree that there is a significant relationship between the Sinhalese and the Bengalis and South Indian Tamils and that there is a significant genetic relationship between Sri Lankan Tamils and Sinhalese, them being closer to each other than other South Asian populations.This is also supported by a genetic distance study, which showed low differences in genetic distance between the Sinhalese and the Bengali, Tamil, and Keralite volunteers. 
Sinhalese people are closely related to other South Asians (Indians) as well as closely related to the broader West-Eurasian clade, including Europeans, Middle Easterners, especially Iranians. Sinhalese are also related to the indigenous Vedda, who are one of the first populations of South Asia and also share deep ancestry with Europeans and Middle Easterners.
A 2017 study conducted by Fumihiko Takeuchi, Tomohiro Katsuya, Ryosuke Kimura and Norihiro Kato showed that the main ancestral population that contributed to the Sinhalese was the "South Asian" component with a significant contribution from the "South Asian and Central Asian" component and smaller contributions from the "Central Asian", "Southeast Asian", "Southeast Asian and East Asian", "East Asian" and "Japanese" components.
Relationship to Bengalis.
An Alu polymorphism analysis of Sinhalese from Colombo by Dr Sarabjit Mastanain in 2007 using Tamil, Bengali, Gujarati (Patel), and Punjabi as parental populations found different proportions of genetic contribution:
A genetic distance analysis by Dr Robet Kirk also concluded that the modern Sinhalese are most closely related to the Bengalis.
This is further substantiated by a VNTR study, which found 70-82% of Sinhalese genes to originate from Bengali admixture:
D1S80 allele frequency (A popular allele for genetic fingerprinting) is also similar between the Sinhalese and Bengalis, suggesting the two groups are closely related. The Sinhalese also have similar frequencies of the allele MTHFR 677T (13%) to West Bengalis (17%).
A test for Y-chromosome DNA haplogroups conducted by Dr Toomas Kivisild on Sinhalese of Sri Lanka has shown that 23% of the subjects were R1a1a (R-SRY1532) positive. Also in the same test 24.1% of the subjects were R2 positive as subclades of Haplogroup P (92R7). Haplogroup R2 is also found in a considerable percentage among Bengali of India. Sample size used was 87 subjects.
A study in 2007 found similar frequencies of the allele HLA-A*02 in sinhalese (7.4%) and North Indian subjects (6.7%). HLA-A*02 is a rare allele which has a relatively high frequency in North Indian populations and is considered to be a novel allele among the North Indian population. This suggests possible North Indian origin of the Sinhalese.
Relationship to Tamils.
Another study by GK Kshatriya conducted in 1995 assessing the 'Genetic affinities of Sri Lankan Populations' found a large genetic contribution from the Tamils of South India, as well as from the Bengali and Vedda populations. The study was carried out using Sinhalese from regions where Sinhala Tamil interactions were higher and older methods compared to other modern and accurate studies.
Relationship to other ethnic groups in Sri Lanka.
A study looking at genetic variation of the FUT2 gene in the Sinhalese and Sri Lankan Tamil population, found similar genetic backgrounds for both ethnic groups, with little genetic flow from other neighbouring Asian population groups. Studies have also found no significant difference with regards to blood group, blood genetic markers and single-nucleotide polymorphism between the Sinhalese and other ethnic groups in Sri Lanka. Another study has also found "no significant genetic variation among the major ethnic groups in Sri Lanka". This is further supported by a study which found very similar frequencies of alleles MTHFR 677T, F2 20210A & F5 1691A in South Indian Tamil, Sinhalese, Sri Lankan Tamil and Moor populations.
A genetic study carried out in 2015 by Lian dang et. on origin of Malay people and other populations of Sri Lanka involving 200 Sinhalese people, 103 Tamil people of Sri Lankan origin, 200 Tamil people of Indian origin and 35 Burgher people calculated the averaged genetic makeup across individuals of each population, which show substantially higher amount of Central Asian ancestry and low South Asian ancestry among Sinhalese compared to both Tamil groups.
Relationship to East and Southeast Asians.
Genetic studies show that the Sinhalese have received some genetic flow from neighboring populations in East Asia and Southeast Asia, such as from the ethnically diverse and disparate Tibeto-Burman peoples and Austro-Asiatic peoples, which is due to their close genetic links to Northeast India. A 1985 study conducted by Roychoudhury AK and Nei M, indicated the values of genetic distance showed that the Sinhalese people were slightly closer to Mongoloid populations due to gene exchange in the past. In regards to comparisons of root and canal morphology of Sri Lankan mandibular molars, it showed that they were further away from Mongoloid populations. Among haplogroups found in East Asian populations, a lower frequency of East Asian mtDNA haplogroup, G has been found among the populations of Sri Lanka alongside haplogroup D in conjunction with the main mtDNA haplogroup of Sri Lanka's ethnic groups, haplogroup M. In regards to Y-DNA, Haplogroup C-M130 is found at low to moderate frequencies in Sri Lanka.
Genetic markers of immunoglobulin among the Sinhalese show high frequencies of afb1b3 which has its origins in the Yunnan and Guangxi provinces of southern China. It is also found at high frequencies among Odias, certain Nepali and Northeast Indian, southern Han Chinese, Southeast Asian and certain Austronesian populations of the Pacific Islands. At a lower frequency, ab3st is also found among the Sinhalese and is generally found at higher frequencies among northern Han Chinese, Tibetan, Mongolian, Korean and Japanese populations. The Transferrin TF*Dchi allele which is common among East Asian and Native American populations is also found among the Sinhalese. HumDN1*4 and HumDN1*5 are the predominant DNase I genes among the Sinhalese and are also the predominant genes among southern Chinese ethnic groups and the Tamang people of Nepal. A 1988 study conducted by N. Saha, showed the high GC*1F and low GC*1S frequencies among the Sinhalese are comparable to those of the Chinese, Japanese, Koreans, Thais, Malays, Vietnamese, Laotians and Tibetans. A 1998 study conducted by D.E. Hawkey showed dental morphology of the Sinhalese is closely related to those of the Austro-Asiatic populations of East and Northeast India. Hemoglobin E a variant of normal hemoglobin, which originated in and is prevalent among populations in Southeast Asia, is also common among the Sinhalese and can reach up to 40% in Sri Lanka.
Skin pigmentation.
In 2008 a study looked at SLC24A5 polymorphism which accounts for 25-40% of the skin complexion difference between Europeans and Africans and up to 30% of skin colour variation in South Asians. The study found that the rs1426654 SNP of SLC24A5, which is fixed in European populations and found more commonly in light skinned individuals than dark skinned individuals (49% compared to 10%), has a frequency of around 55% in the Sinhalese and around 25% in Sri Lankan Tamils. This allele could have arisen in the Sinhalese due to further migration from North India or strong selection factors. 