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BIO NMDCAT Ribonucleic acid (RNA)
nmdcat.online July 3, 2026

97. A patient presenting with severe microcytic anemia is diagnosed with a form of beta-thalassemia. Molecular sequencing reveals a single nucleotide substitution within an intron of the beta-globin gene that generates a novel, functional 3′ splice site. The consequence of this mutation on the resulting mRNA is the

A. Complete omission of the upstream coding exon
B. Retention of a portion of the intron as an aberrant exon sequence
✓
C. Spontaneous degradation of the entire primary transcript within the nucleolus
D. Shift in the reading frame due to failure of poly-A tail attachment

📝 Explanation

The creation of a cryptic splice site inside an intron leads the spliceosome to misidentify the intron boundaries, incorporating junk sequence into the mature mRNA.

📖 Additional Information

  • Complete omission of the upstream coding exon
  • Retention of a portion of the intron as an aberrant exon sequence
  • Spontaneous degradation of the entire primary transcript within the nucleolus
  • Shift in the reading frame due to failure of poly-A tail attachment

The creation of a cryptic splice site inside an intron leads the spliceosome to misidentify the intron boundaries, incorporating junk sequence into the mature mRNA.

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