It is commonly believed that all living organisms follow a single, universal genetic code. As a result, discovering the existence of other genetic codes can be quite surprising.
For evolutionists, the idea of a single universal genetic code is often cited as proof of a common ancestor for all life forms on Earth. Creationists, on the other hand, interpret it as evidence of a single Creator who designed all organisms in a similar way. The identification of alternative genetic codes, therefore, challenges this established framework.
Fundamentals of the Genetic Code
When we refer to the genetic code, we mean the sequence of codons that cells interpret to carry out processes such as protein synthesis. DNA strands are made up of pairs of nitrogenous bases: adenine (A) pairs with thymine (T), and cytosine (C) pairs with guanine (G). During DNA transcription into mRNA, thymine (T) is substituted by uracil (U), while the other nitrogenous bases remain unchanged.
In the mRNA strand, there are four bases: A, C, G, and U. These bases form three-letter sequences known as codons (e.g., GCU, AAC, or UGG). Since there are four bases and each codon consists of three, there are a total of 64 possible codons (43 = 4×4×4 = 64). Nearly all of these codons correspond to a specific amino acid. Cellular mechanisms interpret this code to ensure the correct amino acids are used in the synthesis of the protein required by the cell. Additionally, three of these 64 codons are termination codons (stop codons), which signal the end of the synthesis process.
More Than One Genetic Code?
The standard genetic code, as we understand it, is just one of many. Scientists have found that at least 32 alternative genetic codes exist in nature.1 These codes, like the standard (canonical) version, use the same nitrogenous bases (letters) and codons (words), yet they differ in that some codons correspond to a different amino acid or even carry an entirely different message.
To illustrate, in the nuclear DNA of our cells, the codon ATA (which transcribes to AUA in mRNA) specifies the amino acid isoleucine. In contrast, in mitochondrial DNA (mtDNA), the same codon codes for methionine, a distinct amino acid.2 This demonstrates that the genetic code in mitochondrial DNA differs from the standard code found in nuclear DNA.
A Stop Codon Does Not Always Indicate Termination
The variations also extend to termination (stop) codons. In the mRNA transcribed from nuclear DNA, three stop codons exist: UAG (the amber codon), UAA (the ochre codon), and UGA (the opal codon). These codons do not encode any proteins; instead, they signal the end of protein synthesis, marking the conclusion of a gene.
In 2014, researchers from the Joint Genome Institute (JGI) of the U.S. Department of Energy uncovered an interesting finding. In some bacteria, the opal codon (UGA), actually codes for the amino acid glycine, instead of indicating a stop signal. Similar variations were observed with the amber (UAG) and ochre (UAA) codons.3
The Functioning of Non-Standard Codes
The discovery of alternative genetic codes clarified several previously unexplained issues. Initially, scientists were puzzled by the fact that the genes of certain bacteria were only about 200 base pairs long, while most genes typically consist of 800–900 base pairs. This mystery was resolved when researchers realised that these bacteria utilised a genetic code different from the standard one. It was then revealed that their genes were of the correct length to produce proteins of the appropriate size.4
The role of bacteriophages—viruses that target bacteria to reproduce—was also puzzling to scientists. These viruses are capable of using two stop codons from the bacteria they infect (amber and opal) to produce the amino acids they need. Among these are selenocysteine and pyrrolysine, which are the 21st and 22nd proteinogenic amino acids, and are not produced by vertebrate cells.5
Evidence for Creation and the Creator
The presence of multiple genetic codes, rather than a single universal one, creates a significant issue for evolutionary theory. This is further complicated by the discovery of 33 distinct genetic codes. Any spontaneous mutation in the genetic code, particularly within an animal cell, could result in severe health consequences, including the rapid death of the organism,6 especially if it affects stop codons. Additionally, some genetic codes operate alongside the standard code within the same cell. A key example of this is the mitochondrial DNA found in vertebrates, including humans.
How did the mitochondrial DNA code come to differ from the standard (nuclear) DNA code? Evolutionary science has yet to provide a satisfactory explanation for this. The most plausible conclusion is that the Creator designed all living organisms, including both the standard genetic code and the alternative codes discovered through scientific inquiry. Once again, genetics presents us with compelling evidence of the existence of an Almighty God. As stated in the Book of Psalms: ‘You created my inmost being; you knit me together in my mother’s womb’.7
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Footnotes
- National Center for Biotechnology Information (no date) Taxonomy Browser. Available at: https://www.ncbi.nlm.nih.gov/Taxonomy/Utils/wprintgc.cgi?chapter=tgencodes.
- Creation Ministries International (2012) ‘Is DNA coded information?’, 2 February. Available at: https://creation.com/dna-language-information.
- Science Daily (2014) ‘A glimpse into nature’s looking glass – to find the genetic code is reassigned: Stop codon varies widely’, 22 May. Available at: https://www.sciencedaily.com/releases/2014/05/140522141422.htm.
- Mitchell, E. (2014) ‘Stop-or-Go DNA Codes Reveal Rampant Rule-Breaking in the Language of Life’, Answers in Genesis, 31 May. Available at: https://answersingenesis.org/genetics/stop-or-go-dna-codes-reveal-rampant-rule-breaking-language-life/.
- Ibid.
- Thomas, D. (2022) ‘Evolution’s fatal problem of non-standard genetic codes’, Creation Ministries International, 11 August. Available at: https://creation.com/non-standard-genetic-codes.
- The Bible, New King James Version, 1982, Psalm 139:13.
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