AbstractParasitic B chromosomes invade and persist in natural populations through several mechanisms for transmission advantage (drive). They may contain gene-derived sequences which, in some cases, are actively transcribed. A further interesting question is whether B-derived transcripts become functional products. In the grasshopperEyprepocnemis plorans, one of the gene-derived sequences located on the B chromosome shows homology with the gene coding for the CAP-G subunit of condensin I. We show here, by means of fluorescentin situhybridization coupled with tyramide signal amplification (FISH-TSA), that this gene is located in the distal region of the B24 chromosome variant. The DNA sequence located in the B chromosome is a pseudogenic version of theCAP-Ggene (B-CAP-G). In two Spanish populations, we found active transcription ofB-CAP-G, but it did not influence the expression ofCAP-D2andCAP-D3genes coding for corresponding condensin I and II subunits, respectively. Our results indicate that the transcriptional regulation of theB-CAP-Gpseudogene is uncoupled from the standard regulation of the genes that constitute the condensin complex, and suggest that some of the B chromosome known effects may be related with its gene content and transcriptional activity, thus opening new exciting avenues for research.