XX/XY chimerism in tortoiseshell tomcats – a new case and review of the literature

This study presents a case of a tortoiseshell Maine Coon tomcat exhibiting XX/XY chimerism, a rare genetic condition where two different cell lines are present. Despite this unusual chromosomal makeup, the tomcat was fertile, successfully mating and producing five healthy kittens. Cytogenetic and molecular analyses confirmed the presence of both XX and XY cell lines, with the highest proportion of XX cells found in hair follicles. The findings suggest that tortoiseshell tomcats with XX/XY chimerism can be fertile, and recommend genetic testing for tri-colored male cats before breeding decisions are made.