Q.A single base mutation in a gene may not 'always' result in loss or gain of function. Do you think the statement is correct? Defend your answer.

The statement is correct.

A single base mutation may not always result in a loss or gain of function due to the degeneracy of the genetic code. The genetic code is degenerate, meaning that multiple codons can specify the same amino acid. Therefore, a change in a single base, especially in the third position of a codon, might still result in the incorporation of the same amino acid into the polypeptide chain. Such mutations are termed silent mutations. Since the amino acid sequence of the protein remains unaltered, its three-dimensional structure and biological function are typically unaffec …

The statement that a single base mutation in a gene may not 'always' result in loss or gain of function is indeed correct. Our understanding of molecular biology, particularly the nature of the genetic code and gene structure, provides a clear defense for this.

The core reason lies in the degeneracy of the genetic code. The genetic code is the set of rules by which information encoded in genetic material (DNA or RNA sequences) is translated into proteins by living cells. It consists of a sequence of three nucleotides, called a codon, which specifies a particular amino acid. There are 64 possible codons, but only 20 different amino acids are commonly found in proteins. This means that most amino acids are specified by more than one codon. For example, both CUU and CUC code for the amino acid Leucine.

When a single base mutation occurs, it's called a point mutation. If this point mutation changes a codon to another codon that still codes for the same amino acid, it is termed a silent mutation. In such cases, despite the change in the DNA sequence, the resulting protein sequence remains identical. Since the protein's amino acid sequence is unchanged, its structure and, consequently, its function are also unaffected. This often happens when the mutation occurs in the third position of a codon, as this position is frequently degenerate.

Beyond silent mutations, the location of the mutation within the gene also plays a crucial role:

• Mutations in Non-coding Regions: Genes are not entirely composed of coding sequences. They contain introns (non-coding sequences) interspersed within exons (coding sequences). During gene expression, introns are transcribed into mRNA but are subsequently removed through a process called splicing before the mRNA is translated into protein. Therefore, a single base mutation occurring within an intron typically has no effect on the final protein's amino acid sequence or function. Similarly, mutations in regions outside the gene altogether (intergenic regions) or in regulatory sequences that do not directly code for protein will not alter the protein's structure or function, though they might affect gene expression levels. …

Instead of defending the statement in the abstract, sort possible mutations by TYPE first: a base change at a codon's third position is often silent (same amino acid, no effect on the protein); a change elsewhere may be missense (a different, but sometimes chemically similar, amino acid -- often little effect); only a nons …