Comet Assay Tail Moment

Derive DNA fraction and classic/Olive comet moments from a supplied uniformly area-weighted fluorescence profile and head/tail boundary; segmentation, background correction and genotoxicity interpretation are external.

Description

Summarize a prepared comet fluorescence profile using tail fraction, centroids, and two tail moments.

In a comet assay, electrophoretic migration creates a head and tail pattern from stained cellular DNA. Tail fluorescence relative to total fluorescence is used as a DNA-migration measure. Assay interpretation depends on preparation, controls, image analysis, and the endpoint chosen.^[1]

This tool starts with a one-dimensional profile you have already prepared. It assigns samples before a supplied tail boundary to the head and samples at or after that boundary to the tail. Fluorescence values act as discrete DNA weights at positions in micrometers.

The output tailDnaFraction is a fraction from 0 to 1, not percent DNA. The simple tail moment uses the span from your boundary to the last positive tail sample; the Olive moment uses the separation of head and tail centroids. Both multiply by the fraction rather than its percentage.

When to use Comet Assay Tail Moment

Use it to reproduce explicitly defined profile summaries or check centroid and moment arithmetic after image extraction and a head–tail boundary have already been chosen.

How to use Comet Assay Tail Moment and interpret its calculation

Enter at least two strictly increasing finite profilePositionsMicrometers and an aligned nonnegative dnaFluorescence list.
Enter a finite tailStartMicrometers boundary that leaves positive fluorescence in the head. Keep the profile oriented so the tail extends toward increasing positions.
Run the calculation and read tailDnaFraction, both centroids, tailMomentMicrometers, and oliveTailMomentMicrometers. Match the fraction scaling and tail-span convention before comparing other software.

tail fraction = tail fluorescence/(head + tail fluorescence); centroid = Σ(position × fluorescence)/Σ fluorescence within each region

Samples exactly at the boundary belong to the tail. Head fluorescence must be positive.

tail moment = tail fraction × (last positive tail position − boundary); Olive moment = tail fraction × (tail centroid − head centroid)

No spacing weights, background subtraction, or numerical integration of intensity density are applied.

If no tail fluorescence is present, the implementation sets the tail centroid and last-tail position to the supplied boundary, producing zero for both moments. Zero-fluorescence samples beyond the last positive sample do not extend the simple tail moment.

json

{
  "input": {
    "profilePositionsMicrometers": [
      0,
      1,
      2,
      3
    ],
    "dnaFluorescence": [
      3,
      1,
      1,
      1
    ],
    "tailStartMicrometers": 2
  },
  "output": {
    "tailDnaFraction": 0.3333333333333333,
    "headCentroidMicrometers": 0.25,
    "tailCentroidMicrometers": 2.5,
    "tailMomentMicrometers": 0.3333333333333333,
    "oliveTailMomentMicrometers": 0.75
  }
}

Multiplying all fluorescence weights by the same positive constant preserves the outputs. Tail-free profiles are accepted if head mass is positive. A boundary at or before all signal leaves no positive head and is rejected; a boundary beyond the profile can return a zero-tail summary.

Limitations and assumptions

No image import, cell segmentation, background correction, calibration, damage classification, or assay statistics are performed. The tool cannot verify that fluorescence is proportional to DNA or that the chosen boundary is appropriate.

Unequal spacing is not accounted for: supply consistent per-bin weights rather than uncorrected intensity densities. Different tail-length origins or percent-based moment conventions can differ from these outputs by geometry or a factor of 100.

Alternative or Complementary methods

Compare these per-profile summaries with assay controls and replicate distributions using an appropriate analysis. If subsequent concentration endpoints are needed, NOEC selection or a benchmark model requires separately derived effect data and statistical inputs.

References

Test No. 489: In Vivo Mammalian Alkaline Comet Assay (2016) — Organisation for Economic Co-operation and Development

Similar or alternative tools

NOEC
Summarize concentration-wise significance tests produced by a separate assay analysis.
Continuous BMD
Calculate a benchmark from an externally fitted continuous-response model when suitable for the endpoint.