Loggerhead sea turtles (Caretta caretta) act as sentinels at the wildlife–human interface, carrying antimicrobial-resistant and zoonotic pathogens with direct relevance to One Health. Genetic variation is examined across six nesting areas in Greece using 51 archived tissue samples. Two genetic markers are analysed: MHC genes, which govern immune response and reflect disease resilience, and mitochondrial DNA (D-loop), which reveals evolutionary relationships. Through DNA extraction, PCR, gel electrophoresis, sequencing, and phylogenetic analysis, the project compares allelic diversity and phylogenetic structure across sites, with the aim of understanding population connectivity and isolation among Greek loggerhead nesting populations.