ORF Finder: Gene Prediction Across Reading Frames

DNA Sequence

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Sequence length 90 bp

Minimum ORF length 15 aa

Reading Frame

Results

ORFs found

Longest ORF

0 aa

GC content

No ORFs yet — generate a sequence.

How it works

A gene-coding region in DNA is read as consecutive, non-overlapping triplets (codons). Because a sequence has no built-in "start point," a computer must check all 3 possible offsets on the forward strand and all 3 on the reverse-complement strand — 6 reading frames in total — for a stretch that looks like a real gene: an open reading frame (ORF).

ORF rule (simplified gene-finding model):
  scan codons until ATG (start, codes Met)
  keep reading codons → translate to amino acids
  stop at first TAA / TAG / TGA (stop codon)
  ORF length = codons between start and stop (in aa)

This simulator builds the reverse complement (A↔T, G↔C, then reverses the strand) for frames −1/−2/−3, then applies that scan at all 6 offsets using the standard genetic code table. Each match is mapped back onto its original position in the double helix and lit up in that frame's color.

Random sequence — draws a new sequence uniformly over A/T/G/C at the chosen length.
Sequence length — longer sequences statistically contain more (and longer) ORFs by chance alone, which is why real gene-finders also score against known gene models rather than length alone.
Minimum ORF length — filters out short runs that are almost certainly noise; random DNA produces plenty of short ATG...stop matches that are not real genes.
Reading frame — isolate one frame to see exactly which triplets were read, or show all 6 to compare frame density at once.

Real-world relevance: this greedy 6-frame ORF scan is the first-pass filter inside real gene-prediction tools (e.g. NCBI ORFfinder, Prodigal) before statistical and homology-based scoring narrows candidates down to actual genes.

A T G C

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