chimerism tetragametic chimerism 46,XX/46,XY chimerism A rare, sex chromosome condition characterized by the two different haploid sets of maternal and paternal chromosomes and variable phenotype - from male or female genitalia, to different degrees of ambiguous genitalia, and often infertility. Also, in the cases of monochorionic dizygotic twins, it can be confined to blood of both twins. 46,XX/46,XY