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:

• Missense mutation: A single - nucleotide substitution results in a codon that codes for a different amino acid. Here, the DNA sequence changes from TTG to TCG. When transcribed to mRNA (assuming the DNA is the template strand, TTG would transcribe to AAC and TCG to AGC). AAC codes for asparagine and AGC codes for serine. So, one amino acid is replaced by another.
• Nonsense mutation: Causes a premature stop codon. But there is no indication of a stop codon formation here.
• Silent mutation: The nucleotide change does not result in an amino - acid change. But in this case, the amino acid changes.
• Frameshift mutation: Caused by insertions or deletions (not substitutions) that shift the reading frame. Here, it is a substitution.

Answer:

missense