Question

a mutation causes a sequence of dna that has the nucleotides ttg to be changed to tcg. the resulting protein has a different sequence of amino acids. which type of mutation is this?
○ missense
○ nonsense
○ silent
○ frameshift

Explanation:

1. Recall mutation types:

• Missense: Single nucleotide change (point mutation) that changes the amino acid coded (since DNA codon changes, mRNA codon changes, leading to different amino acid, as seen here with TTG→TCG changing the codon, hence amino acid sequence).
• Nonsense: Changes to a stop codon (not here).
• Silent: Codon changes but amino acid stays same (not here, as amino acid sequence differs).
• Frameshift: Insertion/deletion of nucleotides, shifting reading frame (not a single - nucleotide substitution like here).

1. The mutation here is a point mutation (single nucleotide change: T→C in first position of TTG→TCG) that changes the amino acid sequence, matching missense.

Answer:

A. missense