The Triplet Genetic Code had a Doublet Predecessor
<|reference_start|>The Triplet Genetic Code had a Doublet Predecessor: Information theoretic analysis of genetic languages indicates that the naturally occurring 20 amino acids and the triplet genetic code arose by duplication of 10 amino acids of class-II and a doublet genetic code having codons NNY and anticodons $\overleftarrow{\rm GNN}$. Evidence for this scenario is presented based on the properties of aminoacyl-tRNA synthetases, amino acids and nucleotide bases.<|reference_end|>
@article{patel2004the,
    title={The Triplet Genetic Code had a Doublet Predecessor},
    author={Apoorva Patel},
    journal={Journal of Theoretical Biology 233 (2005) 527-532},
    year={2004},
    archivePrefix={arXiv},
    eprint={q-bio/0403036},
    primaryClass={q-bio.GN cs.CE q-bio.BM quant-ph}
}