What happens to organisms with mutations at the first or second positions of codons?

Mutations at the first or second positions of codons tend to have a significant impact on the protein that is produced. The genetic code is composed of triplets of nucleotides known as codons, each encoding a specific amino acid. The first two positions of a codon are crucial for determining which amino acid is specified.

When a mutation occurs in these positions, it often results in a change in the amino acid sequence of the protein, which is termed a non-synonymous change. This change can affect the protein's structure, function, and overall stability, potentially leading to more pronounced phenotypic effects. In contrast, mutations at the third position of codons are often synonymous, meaning that they do not change the amino acid and usually have a minimal impact on protein function.

Therefore, the characteristic of being prone to result in non-synonymous changes is a key reason why mutations in the first or second positions are particularly important in the study of evolutionary biology and molecular genetics.