Question

Exposure to a mutagen caused the following DNA change within exon #1 of a gene. What type of mutation is this?

Wildtype sequence

template DNA strand 3’ TACAGTGGGTTC 5’   

coding DNA strand 5’ ATGTCACCCAAG 3’   

Mutant Sequence

template DNA strand 3’ TACAATGGGTTC 5’

coding DNA strand 5’ ATGTTACCCAAG 3

a missense mutation

a silent mutation

an exonic mutation

a frameshift mutation

a nonsense mutation

Answer 1

In the given Wild type DNA coding sequence the second codon is TCA while in mutant DNA coding sequence second codon is TTA. Apart from these all the other codons in both sequences are same.

The nucleotide C of second codon of Wild type sequence is replaced with a T in mutant sequence.

This type of mutation in which only one nucleotide is replaced is called point mutation.

Originally codon for TCA, mRNA will be UCA while for TTA will be UUA. UCA codes for Serine while UUA codes for Leucine.

So, in place of Serine, amino acid leucine is added in second position in mutant gene. Such point mutation in which the amino acid in orginal gene is replaced to another nucleotide due to replacement of one nucelotide is called 'missense mutation'.

So, correct answer is 'a missense mutation'.

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