Impact of theta correction in siblingship testing

Area of Science:

• Population genetics
• Forensic science
• Genetic genealogy

Background:

• Genetic relationship testing requires robust population data, with extensive Short Tandem Repeat (STR) data collected globally.
• Limited research addresses population substructure's impact on genetic relationship testing, especially at local levels.
• Population substructure, a proxy for co-ancestry, is corrected using the theta (θ) coefficient, often assessed broadly.

Purpose of the Study:

• To investigate the impact of population substructure on genetic relationship testing.
• To highlight the challenges in accurately estimating co-ancestry at local levels.
• To demonstrate how incorrect theta correction affects kinship calculations and outcomes.

Main Methods:

• Analysis of population substructure at various geographical scales.
• Evaluation of the effect of local population substructure on co-ancestry estimation.
• Assessment of the impact of theta correction factor choice on genetic relationship testing results.

Main Results:

• Local infrastructure, geographic, and sociocultural factors significantly influence co-ancestry estimation.
• Small communities exhibit greater population substructure than large-scale studies capture.
• Incorrect theta values substantially alter genetic relationship test outcomes.

Conclusions:

• Current methods may not adequately address local population substructure in genetic relationship testing.
• There is a lack of conservative approaches for uncertainty in kinship testing, unlike in forensics.
• Recommendations are provided for communicating results, particularly for individuals in legal or administrative proceedings.