This paper challenges the assumption that it is possible to combine the genetic data from both types of markers into a single likelihood ratio. This paper demonstrates that although the genetic evidence obtained from these markers is appropriate for individual probability calculations, mitochondrial DNA (mtDNA) and nhY data are not; consequently, joining the evidential value of the two types of markers is generally inconsistent. The combination of likelihood ratios from the two sources of data should be avoided, since it is generally inconsistent, is statistically heterogeneous, and is prone to strong biases. In contrast, reporting separately the results of the analyses from the two types of evidence, along with the distinct theoretical and statistical frameworks underlying them, is a sound way to avoid misunderstandings in presenting evidence in court. The assumption of noninvolvement of relatives must be clearly and explicitly stated, and its acceptance must be left to the court. 23 references