Mitochondrial DNA (mtDNA) is DNA found inside mitochondria. mtDNA is inherited solely from the maternal lineage in humans. mtDNA is composed of two strands, totaling 16,569 base pairs in length. Within this DNA, there are 37 genes responsible for encoding various molecules necessary for mitochondrial function. These genes include 2 ribosomal RNAs (rRNAs), 22 transfer RNAs (tRNAs), and 13 polypeptides.