Gene Mutations and Their Effects — NEET Biology

Correct answer: B — S1, S3, and S5 are correct

Let's evaluate each statement regarding mutations and the genetic code: S1. A silent mutation, such as the change from UAU to UAC (both coding for Tyrosine), results in no change in the amino acid sequence of the polypeptide due to the degeneracy of the genetic code. This statement is correct. Both UAU and UAC code for Tyrosine (Tyr), so changing one to the other is a silent mutation, enabled by the degeneracy of the genetic code. S2. A missense mutation occurs when a single base change leads to the formation of a premature stop codon, thereby shortening the polypeptide chain. This statement is incorrect. A single base change leading to a premature stop codon is known as a *nonsense* mutation, not a missense mutation. A missense mutation results in a different amino acid. S3. The change of a single base pair in the gene for the beta-globin chain from GAG to GUG, causing Glutamate to change to Valine, is an example of a missense mutation. This statement is correct. This is the classic example of point mutation causing sickle cell anemia, where one amino acid (Glutamate) is replaced by another (Valine), which is a missense mutation. S4. Frameshift mutations are always more severe than point mutations because they alter the reading frame from the point of insertion or deletion, affecting all downstream amino acids. This statement is incorrect. While frameshift mutations (insertion/deletion of one or two bases) often have severe consequences by altering the entire downstream sequence, not all point mutations (single base changes) are less severe. For example, a nonsense mutation (a type of point mutation) can lead to premature termination and a severely truncated, non-functional protein, which can be as severe as or even more severe than some frameshift mutations depending on the location. Also, point mutations like the one causing sickle cell anemia can be very severe. S5. The non-overlapping nature of the genetic code means that a point mutation (single base change) will only affect the amino acid coded by that specific codon, without impacting adjacent codons. This statement is correct. Because the code is non-overlapping, each nucleotide belongs to only one codon. Therefore, a change in a single nucleotide within a codon will only affect that particular codon's amino acid, not the amino acids coded by the codons immediately before or after it. Therefore, statements S1, S3, and S5 are correct. The tested concept is the different types of point mutations (silent, missense, nonsense) and their effects, as well as the implications of the degeneracy and non-overlapping nature of the genetic code on mutation outcomes.