Structure-informed clustering for population stratification in association studies

BACKGROUND

Identifying variants associated with complex traits is a challenging task in genetic association studies due to linkage disequilibrium (LD) between genetic variants and population stratification, unrelated to the disease risk. Existing methods of population structure correction use principal component analysis or linear mixed models with a random effect when modeling associations between a trait of interest and genetic markers. However, due to stringent significance thresholds and latent interactions between the markers, these methods often fail to detect genuinely associated variants.

RESULTS

To overcome this, we propose CluStrat, which corrects for complex arbitrarily structured populations while leveraging the linkage disequilibrium induced distances between genetic markers. It performs an agglomerative hierarchical clustering using the Mahalanobis distance covariance matrix of the markers. In simulation studies, we show that our method outperforms existing methods in detecting true causal variants. Applying CluStrat on WTCCC2 and UK Biobank cohorts, we found biologically relevant associations in Schizophrenia and Myocardial Infarction. CluStrat was also able to correct for population structure in polygenic adaptation of height in Europeans.

CONCLUSIONS

CluStrat highlights the advantages of biologically relevant distance metrics, such as the Mahalanobis distance, which captures the cryptic interactions within populations in the presence of LD better than the Euclidean distance.

Population genetic structure of Semisulcospira gottschei: simultaneous examination of mtDNA and microsatellite markers

Semisulcospira gottschei is an Asian endemic species inhabiting Korea and China. However, genetic structure analysis of the resource management of this species has not been performed. To investigate the genetic diversity among populations, microsatellites can be used to determine the geographic origins of marine and freshwater species. This study investigated the genetic structures of the Korean and Chinese populations of S. gottschei based on mitochondrial DNA (mtDNA) Cytochrome oxidase subunit I (COI) and polymorphic microsatellite loci developed from Semisulcospira coreana. Analysis of the mtDNA COI sequence revealed 43 haplotypes, which indicated no gene flow between the Korean and Chinese populations. To further elucidate the genetic structures of the Korean and Chinese populations, the population genetics of S. gottschei were analyzed using nine microsatellite markers. The genetic diversity analysis showed an average of 5.25 alleles per locus, with an average allelic richness of 4.02. Excessive homozygosity was found at all loci, which was expected to be due to the presence of null alleles at all loci. Populations of S. gottschei formed two separate clusters according to pairwise F_ST and AMOVA. Also, the UPGMA tree, PCA, STRUCTURE, and GeneClass indicated separation of the 11 populations into two clusters: Korea and China. These results have potential use in the management, restoration, and distinction of the origin country of populations.

Genetic diversity and population structure of the endangered fish Pseudobagrus brevicorpus (Bagridae) using a newly developed 12-microsatellite marker

BACKGROUND

Pseudobagrus brevicorpus is an endangered species in Korea. The development of genetic markers and genetic information regarding the populations of this species are needed to establish conservation strategies.

OBJECTIVE

As part of the conservation of P. brevicorpus, a 12-microsatellite marker was developed using next-generation sequencing (NGS) to provide current genetic population information.

METHODS

Microsatellites from P. brevicorpus were identified by NGS analysis. Genetic diversity and genetic structure analysis of six populations (Seojeong Stream [SJ], Gokgang Stream [GK], Jaho Stream [JH], Daega Stream [DG], Nam River [NG], and Deokcheon River [DC]) of P. brevicorpus were conducted using the newly developed microsatellite marker.

RESULTS

NGS generated 10,347,578 reads and identified 659,507 simple sequence repeats. Twelve microsatellites were successfully amplified and verified in 30 individuals of P. brevicorpus. The genetic diversity of the six P. brevicorpus populations in terms of the number of alleles ranged from 3.667 to 7.111. All populations except DG deviated significantly from Hardy-Weinberg equilibrium (HWE) at one or more loci. The genetic distances of the six populations showed the closest relationship between the SJ and GK populations (independent Stream populations), and there was a close relationship with the JH population among the Nakdong River. Structure analysis showed that P. brevicorpus is largely divided into two groups.

CONCLUSIONS

The developed microsatellite marker will be used to provide basic genetic data of P. brevicorpus. Genetic diversity and structure analysis of the population will provide useful information for conservation management of P. brevicorpus.