The substitution of a single nucleotide in mRNA during transcription is known as a point mutation. This change in the mRNA sequence can affect the amino acid sequence in the resulting polypeptide during translation in one of the following ways:1. Silent mutation: If the substituted nucleotide still codes for the same amino acid as the original nucleotide, it is called a silent mutation. In this case, the amino acid sequence in the polypeptide remains unchanged. This occurs because the genetic code is degenerate, meaning that multiple codons sets of three nucleotides can code for the same amino acid.2. Missense mutation: If the substituted nucleotide codes for a different amino acid, it is called a missense mutation. This change can lead to an altered amino acid sequence in the polypeptide. The effect of a missense mutation on the protein function depends on the chemical properties of the original and substituted amino acids and their role in the protein structure. If the change is conservative i.e., the new amino acid has similar properties to the original one , the protein function might not be significantly affected. However, if the change is non-conservative, it can lead to a loss of function or altered function of the protein.3. Nonsense mutation: If the substituted nucleotide results in a premature stop codon, it is called a nonsense mutation. This type of mutation leads to a truncated polypeptide, as translation is terminated prematurely. The resulting protein is usually non-functional or has a significantly altered function, as it lacks a portion of its amino acid sequence.In summary, the substitution of a single nucleotide in mRNA during transcription can affect the amino acid sequence in the resulting polypeptide during translation in various ways, ranging from no effect silent mutation to significant changes in protein function missense and nonsense mutations .