The P{lacW}Cyt-c-pk13905 insertion is lethal over Df(2L)Exel6039 (a deficiency that removes both Cyt-c-p and Cyt-c-d) and this lethality can be rescued by transgenic expression of either Cyt-c-p or Cyt-c-d. However, the lethality of P{lacW}Cyt-c-pk13905 homozygotes cannot be rescued, suggesting that in addition to lethality associated with the insertion, the chromosome carries an additional unrelated lethal mutation.