Analytical expectations for ancestry junction accumulation in admixed genomes.

Area of Science:

• Population Genetics
• Genomics
• Evolutionary Biology

Background:

• Human history is marked by complex demographic events that shape genetic variation.
• Admixed populations possess unique genetic signatures resulting from multiple ancestral sources.

Purpose of the Study:

• To develop a generalizable model for reconstructing the recent evolutionary history of admixed populations.
• To leverage ancestry switches (recombination breakpoints) to understand admixture dynamics.

Main Methods:

• Developed a discrete model of admixture based on ancestry switches.
• Derived analytical expectations for switch counts based on recombination rate, heterozygosity, and population size.
• Incorporated population-specific recombination maps.
• Validated the model using forward-time simulations and empirical data from the 1000 Genomes Project.

Main Results:

• Simulations showed close agreement between theoretical predictions and model-based switch counts.
• Observed minimal variability in switch counts across replicates, indicating model robustness.
• Model-based switch counts aligned with empirical data from African American individuals, estimating an initial African ancestry proportion of 0.85 for chromosome 1.

Conclusions:

• The developed model provides a novel method for studying the interplay of recombination and demography in admixed populations.
• Ancestry switches serve as a valuable tool for reconstructing population history without needing distinct parental source populations.