ND-23⁶⁰¹¹⁴/ND-23^G14097 transheterozygotes show a progressive decrease in adult climbing capacity, a progressive bang-sensitive paralysis and enlarged mitochondria in their PPM2 neurons, as compared to controls; ND-23⁶⁰¹¹⁴ homozygous and ND-23⁶⁰¹¹⁴/ND-23^G14097 transheterozygous adults also show significant signs of neurodegeneration (i.e brain vacuolization), as compared to either heterozygous controls. Transheterozygous progeny from ND-23⁶⁰¹¹⁴/+ mothers and ND-23^G14097/+ fathers show more severe defects in lifespan, climbing activity and neurodegeneration than progeny from the reciprocal cross between ND-23⁶⁰¹¹⁴/+ fathers and ND-23^G14097/+ mothers, which suggests a maternal effect and which seems to be due to differences in the mitochondrial DNA of the ND-23⁶⁰¹¹⁴ stock.