Point mutations are changes in the base sequence that can have a significant impact on phenotype.

• A. Changes in the base genes that can have a significant impact on phenotype.
• B. Changes in the number of chromosomes.
• C. Changes in the intron sequences only.
• D. No effect on phenotype.

Answer: (A)

Point mutations are single-base changes in the DNA sequence that can alter the information encoded by a gene. Because the genetic code translates those bases into amino acids, a single nucleotide change can change an amino acid, create a stop signal, or affect regulatory regions, leading to a different protein or different gene expression and, consequently, a change in phenotype. That’s why describing them as changes in the base sequence that can significantly impact phenotype is the best fit. The other statements point to different types of mutations (chromosome number changes), limit mutations to introns, or claim no effect on phenotype, which don’t capture how nucleotide-level changes can influence traits.