Question

a) Which DNA mutation is more likely to have a detrimental effect on the protein it codes for: a 2 base pair deletion from the middle of the coding sequence of a gene, or a 12-base pair deletion from the same region of the gene? Explain why?

b) Would the outcome be different if the deletions happened within the gene’s intron? Explain why?

Answer 1

A)

Answer : Considering it is an indel mutation, the deletion of 2 basepair than 12 basepair will have more detrimental effect on proteins.

EXPLANATION

INDEL MUTATION

• Insertion deletion mutations (indel mutation) are created by the insertion or deletion of nucleotides, which is less than 1Kb in size.
• Indel mutation is two types,

1 FRAME SHIFT MUTATION

1) It is the deletion or insertion of nucleotides not multiple of 3.

2) A codon is represented as 3 nucleotides, which codes 1 amino acid during translation.

3) So if 1 or 2 basepairs deleted the reading frame will completely changed from the original genomic DNA.

4) Mostly it will leads to complete loss of original function and may get new detrimental function also.

5) Mostly this mutation can be identified from the phenotype of organism.

Example :

-AAA AGC GAG UGC AUG GGG AGC-

If the GC in second codon deleted, the result will be

-AAA AGA GUG CAU GGG GAG-

It shows a complete deviation from the original sequence, so here the number of aminoacid and coding sequence will be completly changed.

2 INFRAME MUTATION

1) This mutation resulted from the deletion or insertion of nucleotides, which are multiple of 3

Example, deletion or insertion of 3, 6, 9, 12 etc nucleotides.

2) Inframe mutation will change the number of amino acids but the reading frame will be the same.

3) Mostly the translated protein shows its partial or almost full function based on number of deletion of nucleotides.

Example :

-AAA AGC GAG UGC AUG GGG AGC-

If the second and third codon deleted, the result will be as follows,

-AAA UGC AUG GGG AGC-

B)

Answer : If the deletion occur in the intronic region it will not have any effect on Protein.

EXPLANATION

1) Introns are the non coding part of gene, ie, which does not code for any amino acids. So this gene sequence does not expressed in the proteins.

2) After Transcription, the pre mRNA is formed having both intron and coding exons regions.

3) After that a modification called Splicing, the intron regions are splicing out so only the exons will be translated.

So the deletions or insertions in the introns will not generally expressed in proteins.