For a long time, biologists believed that our DNA resided only in the nucleus, the large organelle acting as the control centre in our cells. It wasn't until 1963, when scientists Margrit and Sylvan Nass at Stockholm University discovered DNA fibres in mitochondria using electron microscopy. Our mitochondrial DNA (mtDNA) accounts for a small portion of our total DNA. In fact, it contains just 40 of the 20,000 to 25,000 protein-coding genes in our body, however, it is notably distinct from nuclear DNA. Unlike nuclear DNA, which comes from both parents, mitochondrial DNA comes only from the mother. In this podcast, I explain the significance of this key biological difference, and explore what other roles this fascinating molecule plays in our bodies. (With thanks to our sponsor 'Curriculum Press' for providing content for this podcast)