The avian mitochondrial genome

Apart from the bulk of the genes located on the chromosomes within the nucleus, there are also 

Unhybridised region EcoRI-family minor domain X/ oI-family domain 

DNA-sequencing methods had been developed in the mid-1970s, the small size of mitochondrial DNAs made them attractive subjects for sequencing. The first complete sequence to be resolved was that of the human mitochondrial genome (Anderson et al, 1981). Since then several vertebrate mitochondrial genomes have been sequenced, including that of the domestic fowl (Desjardins Morais, 1990) and much of the quail (Desjardins Morais, 1991) and duck (Ramirez, Savoie Morais, 1993). 

In order to synthesise proteins, mitochondria require ribosomes, together with a full complement of tRNAs. To use all of the codons, making allowance for wobble in the third position of the codon, it would be expected that 32 different tRNAs would be required. Mitochondrial translation apparatus has been found not only to have slightly different codon usage (see Table 8.5) but also to use a more extensive wobble ( superwobble ) than the cytoplasmic system, and this enables them to incorporate all the amino acids with only 22 tRNAs. 

---