Question

Choose the correct answer from the alternative given:
A DNA sequence undergoes three subsequent point mutation which results in subsequent changes in the transcription of mRNA as shown below:
Original mutation: AUG CAU CUC ACG GAU UAG
Point mutation 1: AUG CAU CUU ACG GUA UAG
Point mutation 2: AUG CAU GCU UAC GGU AUA
Point mutation 3: AUG CAU GCU UAA GGU AUA
Select the correct sequence of a point mutation that occurred in the DNA.
(a) Missense mutation - Frameshift mutation - Nonsense mutation
(b) Silent mutation - Nonsense mutation - Frameshift mutation
(c) Silent mutation - 4Frameshift mutation - Nonsense mutation
(d) Missense mutation - Frameshift mutation - Silent mutation

Answer 1

Hint: It is a genetic mutation caused by the addition or deletion of nitrogenous bases in DNA or mRNA. Which can either change the resulting amino acid or not based on the mutation. The mutation can also change the amino acid coding codon to stop coding codon.

Complete step by step answer:
DNA sequence:

mRNA original mutation sequence:

Silent Mutation:
In this type of mutation single base nucleotide substitution is in between the codons which cause no change in amino acid.
Here, in the given sequence CUC changes to CUU where both codes for leucine amino acid. In other, GAU code for aspartate changes to GUA which encode to valine.

Frameshift mutation:
As these shifts the reading frame of codons from the location of change onward to deletion could also be neutralized by one addition or the other way around.
Here, in the given sequence loss of one nucleotide that is ‘G’ causes change in codon from GUA to GGU.

Nonsense mutation:
This type of mutation causes accidental change into stop codons which cause the protein chain to be cut short.
Here, UAA is a stop codon.

So, the correct answer is, ‘Silent mutation - 4Frameshift mutation - Nonsense mutation.’

Additional information:
- Spontaneous mutation occurs naturally without any cause.
- The rate of spontaneous mutation is extremely slow eg- Methylation followed by deamination of cytosine.
- Rate of spontaneous type mutation is higher in eukaryotes than prokaryotes.
- Some genes show a high rate of mutation such genes are called mutable genes.Highly mutable sites within a gene are referred to as hot spots.
- A mutation occurring in somatic cells is called somatic mutation. In asexually reproducing species somatic mutations transmit from one progeny to the next progeny.
- When a mutation occurs from the normal/wild type allele to mutant allele are referred to as forwarding mutation.
- When a mutation occurs within the reverse direction that's from mutant allele to the normal/wild type allele are referred to as a reverse mutation.

Note:
- Point mutations are the common sort of point mutation and are also known as base- pair substitution.
- Change in a single nucleotide base pair.
- Point mutation can be categorized into three types: Silent mutation, Missense mutation, Nonsense mutation.