ADMIXMAP

ADMIXMAP models ancestry of genomic loci and maps ancestry-linked disease susceptibility loci in admixed populations, including African-American cohorts, using marker genotypes and trait data.

Key Features:

• Admixture modeling: Models genetic admixture using marker genotypes to detect loci where allele frequencies and disease risk differ between ancestral populations that originated on different continents.
• Statistical power and mapping resolution: Optimized for high power in admixture mapping; for example, in an African American two-way admixture (0.8/0.2) with an ancestry crossover rate of 2 per 100 cM, a study of 800 affected individuals can achieve ~90% power to detect loci with significant risk ratios.
• Bayesian inference: Uses Bayesian computational methods to infer locus ancestry from multilocus marker data.
• Affected-only study designs: Supports affected-only designs that leverage prior information about allele frequencies conditional on locus ancestry.
• Integration with population data: Combines data from unadmixed and admixed populations to estimate ancestry-specific allele frequencies within the study population.
• Linkage analysis efficiency: Simulation studies reflective of African American genetic structure indicate that ~60% of information can be extracted using markers with ancestry information content of 36% at 3-cM spacing, comparable to classic linkage studies.
• Strategic marker use: Recommends moderate-density marker genome scans for initial searches followed by regional marker saturation in candidate linkage regions.

Scientific Applications:

• Disease susceptibility mapping: Identifying loci associated with disease risk that differ in frequency between ancestral populations in admixed cohorts.
• Genetic linkage studies: Enhancing linkage signal detection and resolution by inferring locus ancestry and optimizing marker spacing and density.
• Population genetics research: Characterizing genetic diversity, ancestry proportions, and structure in admixed populations to study evolutionary and demographic dynamics.

Methodology:

AdmixMap applies Bayesian inference to multilocus marker genotypes to estimate locus ancestry, integrates admixed and unadmixed population data to estimate ancestry-specific allele frequencies, and uses simulation-based analyses to evaluate marker information content and mapping power.