What is a point mutation and how can it affect a gene's function?

What is a point mutation and how can it affect a gene's function?

• A. A chromosomal rearrangement
• B. A single nucleotide change; can alter codon, amino acid, or stop/start signals affecting function
• C. A mutation that only occurs in germ cells
• D. A mutation that has no effect

Answer: (B)

A point mutation is a single nucleotide change in the DNA sequence. Because genes are read in codons, changing one base can shift the meaning of that codon, potentially swapping one amino acid for another (a missense change), creating a stop codon that truncates the protein (a nonsense change), or altering the start codon and changing where translation begins. These changes can affect the protein’s size, structure, and function. Sometimes the new codon still codes for the same amino acid (a silent mutation), so function may stay the same, though it can also subtly influence how much protein is made or how it folds. Larger-scale changes like chromosomal rearrangements aren’t point mutations, and mutations don’t always have no effect—many point mutations can alter function, though some are neutral.

A point mutation is a single nucleotide change in the DNA sequence. Because genes are read in codons, changing one base can shift the meaning of that codon, potentially swapping one amino acid for another (a missense change), creating a stop codon that truncates the protein (a nonsense change), or altering the start codon and changing where translation begins. These changes can affect the protein’s size, structure, and function. Sometimes the new codon still codes for the same amino acid (a silent mutation), so function may stay the same, though it can also subtly influence how much protein is made or how it folds. Larger-scale changes like chromosomal rearrangements aren’t point mutations, and mutations don’t always have no effect—many point mutations can alter function, though some are neutral.