Table 1. Relative volume of mitochondria in TK2^+/+ and TK2^−/− mice.

Age (days)	Relative Volume (%)
	TK2+/+	TK2−/−
7	20.5±3.2	24.0±1.5
12	27.8±0.2	45.5±4.5*

A stereological method was used to determine the volume density of the mitochondria in the cytoplasm from digital electron images taken by a Morada camera. Three different animals were analysed for each genotype and age. For each animal 9 randomly taken images from two different sections (18 images/animal) were counted making a total of 54 images/group. The P-value for statistical comparison (two-tailed unpaired Student’s t-test) between TK2^+/+ and TK2^−/− of the same age is shown, *p≤0.05.