Frameshift Mutations and Reading Frame — NEET Biology
✅ Asked in NEET 2017If there are 999 bases in an RNA that code for a protein with 333 amino acids, and the base at position 901 is deleted (making it 998 bases), how many codons will be altered? (NEET 2017)
If there are 999 bases in an RNA that code for a protein with 333 amino acids, and the base at position 901 is deleted (making it 998 bases), how many codons will be altered? (NEET 2017)
Answer & NCERT explanation
Correct answer: B — 33
When base 901 is deleted, it causes a frameshift mutation. Originally 999 bases = 333 codons. After deletion at position 901, all codons from position 301 onwards (901÷3 = 300.33, so from 301st codon) will be altered due to the reading frame shift. From codon 301 to 333, there are 33 codons that will be affected. This demonstrates how frameshift mutations affect multiple codons downstream of the deletion point.
Read more NCERT concept on the PYQ
The conclusion from the above exercise is very obvious. Insertion or deletion of one or two bases changes the reading frame from the point of insertion or deletion. However, such mutations are referred to as
Frameshift mutations occur when one or two bases are inserted or deleted from DNA, causing a shift in the reading frame from that point onward. This changes every codon downstream, usually producing nonfunctional proteins. Students often confuse frameshift mutations with point mutations—point mutations change only one amino acid, while frameshifts alter the entire sequence after the mutation site. Remember: deletion or insertion of bases (not multiples of 3) shifts the reading frame, whereas deletion/insertion of 3 or 6 bases maintains the frame. NTA tests this because it's fundamental to understanding how mutations affect protein synthesis and gene expression.
What does NCERT say about conclusion from above exercise?
Has this concept appeared in NEET?
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