## Friday 3 May 2024

### A Comprehensive Guide on How to Calculate the Size of a DNA Band on a Gel

How do scientists determine the size of DNA bands on an agarose gel? In this guide, I will walk you through the step-by-step process of calculating the size in base pairs of a DNA band on an agarose gel.

Blog Bonus: Free information sheet summarising the video and the steps - download.

### Introduction

When working in a lab and running an agarose gel, you may need to determine the size of the DNA fragment, and this information may be crucial for various biological research applications.

This approach is also described in the following video:

### Setting Up the Experiment

Imagine you have loaded a DNA ladder with known sizes in one lane and your DNA sample with an unknown size in another lane of the gel and you get a result that looks like this when the gel has been run.

Before you can calculate the size of your DNA band, you must first label the gel and collect data to create a calibration curve.

### Data Collection and Analysis

By measuring the distances the DNA bands in the ladder (see below) have moved and plotting the log values of their sizes against the distances travelled in millimetres (or you can do it in pixels), you can create a calibration curve. This curve will help you accurately determine the size of the DNA band in your unknown sample.

The image below shows the gel and the data table for the plot.

From the table, you plot the calibration curve.

### Calculating the Size of the DNA Band

After plotting the calibration curve (above) and identifying the distance your unknown band has travelled, you can use the curve to determine the size of the DNA band in base pairs. By following a simple formula involving logarithms, you can convert the log value to the actual size in base pairs.

### Conclusion

Calculating the size of a DNA band on an agarose gel requires careful data collection, analysis, and interpretation. By following the steps outlined in this guide, you can confidently determine the size of DNA fragments in your samples.

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Blog Bonus: Free information sheet summarising the video and the steps - download.