Received: 19 September 2019 Revised: 9 January 2020 Accepted: 10 January 2020 DOI: 10.1111/ahg.12379 ORIGINAL ARTICLE Genetic structure of the ethnic Lao groups from mainland Southeast Asia revealed by forensic microsatellites Suparat Srithawong 1 Kanha Muisuk 2 Metawee Srikummool 3 Narongdet Mahasirikul 4 Saksuriya Triyarach 5 Kamnikone Sriprasert 6 Wibhu Kutanan 1 1 Department of Biology, Faculty of Science, Khon Kaen University, Khon Kaen, Thailand 2 Department of Forensic Medicine, Faculty of Medicine, Khon Kaen University, Khon Kaen, Thailand 3 Department of Biochemistry, Faculty of Medical Science, Naresuan University, Phitsanulok, Thailand 4 College of Local Administration, Khon Kaen University, Khon Kaen, Thailand 5 Faculty of Business Administration and Accountancy, Khon Kaen University, Khon Kaen, Thailand 6 Faculty of Economics and Business Administration, National University of Laos, Vientiane, Lao People’s Democratic Republic Correspondence Wibhu Kutanan, Department of Biology, Faculty of Science, Khon Kaen University, Mittapap Road, Khon Kaen 40002, Thailand. Email: wibhu@kku.ac.th Funding information Naresuan University, Grant/Award Num- ber: R2561B029; Khon Kaen University, Grant/Award Numbers: 6200066, 592T224 Abstract Purpose: Laotians and Lao Isan are widely spread Lao groups who live in Laos and northeastern Thailand, respectively. We explored the genetic structure between them and other ethnic groups from Thailand to clarify historical patterns of admixture between Tai-Kadai and Austroasiatic speakers, and to expand the forensic reference database for the region. Subjects and Methods: We combined new genetic data for 554 individuals from 12 populations, typed for 15 autosomal short tandem repeats, with available data from 14 populations from Thailand, for a total of 1,153 raw genotypes belonging to 26 popu- lations. We calculated forensic parameters and performed various analyses on genetic diversity, genetic structure, genetic admixture, and genetic relationships among the studied populations. Results: Forensic estimators suggest a good power of discrimination with the com- bined power of exclusion ranging from 0.993628 to 0.999991 and a combined power of discrimination value greater than 0.99999999. Generally, the two Laotian groups were genetically similar, but the central Laotians from Vientiane have a closer genetic relationship to the Lao Isan than the northern Laotians from Luang Prabang. The Lao genetic ancestry forms the majority of the Lao Isan genetic makeup, while Austroasi- atic ancestry is present at ∼10%–50%. Conclusions: Lao Isan populations show signs of Lao ancestry and admixture with local Austroasiatic ancestry, which reflect historical migrations from Laos to Thai- land. Lao speakers are genetically more homogeneous than Austroasiatic speakers, suggesting differential historical processes. KEYWORDS admixture, autosomal microsatellites, ethnic Lao, Laos, northeastern Thailand 1 INTRODUCTION The Laotians and Lao Isan are the two major ethnic groups found in present-day Laos and northeastern Thailand, with a census size of ∼4.23 million and ∼15 million, respectively (Simons & Fennig, 2018). Their languages both belong to the Tai-Kadai (TK) family and have been proposed to originate from southern or southeastern Chinese dialects (Premsrirat, Ann Hum Genet. 2020;1–13. © 2020 John Wiley & Sons Ltd/University College London 1 wileyonlinelibrary.com/journal/ahg