Jukes T H
J Mol Evol. 1981;18(1):15-7. doi: 10.1007/BF01733206.
Differences between mitochondrial codes and the universal code indicate that an evolutionary simplification has taken place, rather than a return to a more primitive code. However, these differences make it evident that the universal code is not the only code possible, and therefore earlier codes may have differed markedly from the previous code. The present universal code is probably a "frozen accident." The change in CUN codons from leucine to threonine (Neurospora vs. yeast mitochondria) indicates that neutral or near-neutral changes occurred in the corresponding proteins when this code change took change took place, caused presumably by a mutation in a tRNA gene.
线粒体密码与通用密码之间的差异表明发生了进化简化，而非回归到更原始的密码。然而，这些差异清楚地表明通用密码并非唯一可能的密码，因此早期的密码可能与之前的密码有显著不同。当前的通用密码可能是一种“冻结的偶然”。CUN密码子从亮氨酸变为苏氨酸的变化（粗糙脉孢菌与酵母线粒体的对比）表明，当这种密码变化发生时，相应蛋白质中发生了中性或近中性变化，推测这是由一个tRNA基因中的突变引起的。
