Question

Explain what is meant by the phrase “the genetic code is redundant and nearly universal,” and state its significance to evolutionary biology.

Answer 1

The answer to your query is as follows:

The genetic code is redundant.

This statement means that the genetic code is degenerate. It means that out of the 64 codons possible some codons can code for more than one amino acid.

As we know that humans use 20 amino acids to form proteins. To code for these 20 amino acids we have 64 codon combinations available in the form of 4 bases in 3 spots. So, there are more codons available for us than the required amount. This leads to the redundancy or degeneracy and thus, each amino acid has multiple codons.

For example, AAA codes for lysine amino acid. Similarly, AAG also codes for lysine amino acid.

This redundancy plays a very important role in genetic code. It is helpful in the cases of “silent mutations” . It means that if the mutation occurs, then the end amino acid formed will be the same. Therefore, no major changes can occur in the organism after such mutations.

The genetic code is nearly universal.

The genetic code is not completely universal because it shows some minor rare variations or exceptions.For example, mitochondria, the power house of the cells in human uses three codons that normally code as "stop codons" for the amino acids.Thus, it tells the cellular machinery that an amino acid chain is completed.

Some other changes were also observed in the genetic code of the jellyfish and comb jellies. These changes were not found in other animals.

Infact, some bacteria use the sequence UAG to code for pyrrolysine and not to use as a stop codon.

Significance to evolutionary biology

• As stated above, the nearly universal genetic code tells that all the vertebrates share the change in the pattern of the genetic code in the mitochondrial DNA. It strongly suggests that this happened early in the evolution of the vertebrates.
• The minor changes in the genetic code of the Cnidarians and Ctenophores suggests that this group developed this change just after splitting off from other animal groups. But it is believed that all variations were ultimately derived from the standard genetic code of the organisms
• The genetic code is shared by the variety of the organisms found on the earth. It shares an important evidence for the common origin of life on our planet Earth. Many present day species on Earth are likely to be evolved from an ancestral organism that has the genetic code already present in them. The genetic code will remain unchanged in species across generations. Thus, this type of similarity of the code explains the evolutionary process across the present day diverse organisms.

Hope it helps!