Genetic genealogy is a rapidly growing field. The potential for genetics to make genealogical connections and break brick walls is starting to be untapped. This is more so for Latin American and Caribbean societies where limited or non-existent documentation is a reality. This article uses advanced genetic testing to draw genealogies for a particular set of Puerto Rican families, the Sotomayor and Colón families, with connections to the Iberian Pereira lineage. In the critical analysis of the existing fragmented and isolated documentation with advanced genetic testing, mainly Y-DNA, and in its proper historical context, long-standing brick walls have been broken. The study also illustrates, through the prism of genetics, the complex anthroponymy system of Iberian surnames in the American context, which gave a legitimate and significant role to maternal ancestry. As one of the very few instances of a Y-DNA genetic match between two men of different surnames at the edge of genealogical time frames, this study offers insights into the larger use of genetics for genealogy and anthroponymy.