A double-stranded DNA sequence has six possible reading frames due to three frames per strand (forward and reverse, read 5’→3′). The correct answer is option 1.

Question Breakdown

This MCQ evaluates understanding of reading frames in molecular genetics, vital for gene prediction, ORF analysis, and exams like GATE Life Sciences where translation concepts are tested.

Option Analysis

• Option 1: 6
  Correct. Double-stranded DNA has two antiparallel strands. Each strand yields three reading frames (starting at position 1, 2, or 3), totaling six when read 5’→3′ on both.

• Option 2: 3
  Incorrect for double-stranded DNA. This applies only to a single strand (e.g., mRNA), ignoring the complementary strand’s three frames.​

• Option 3: 9
  Incorrect. No biological basis; exceeds the six frames from triplet codons on two strands. Possibly confuses with other concepts like phases.​

• Option 4: 2
  Incorrect. Represents only the two strands, not accounting for three possible starting positions per strand.​

Introduction to Reading Frames

The number of reading frames in double stranded DNA sequence is six, arising from three frames per strand in the 5’→3′ direction. This concept is fundamental in genomics for identifying potential genes via open reading frames (ORFs).

How Six Frames Arise

DNA’s antiparallel strands allow translation from both: forward strand (frames +1, +2, +3) and reverse complement (frames -1, -2, -3). Codons are non-overlapping triplets, so shifting the start by one or two bases creates distinct frames.​​

Applications in Genetics

Bioinformatics tools like ORFfinder scan all six frames to predict proteins from raw sequences. In exams, distinguish from single-strand (3 frames) contexts like mRNA.​