Mitochondrial and plastid genes are maternally inherited, and what's passed down via those genes are pretty well understood (variegation can only be passed down maternally for example, and most physical structure genes are not cytoplastic); Nepenthes do not possess a y-chromosome, so there is no such think as y-linked genes for them. There has not, in fact, been any particular chromosome or gene isolated that we know to determine sex.