How to determine DNA fragment size from this gel

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Discussion Overview

The discussion revolves around determining the size of DNA fragments from a gel electrophoresis image. Participants explore methods for estimating fragment sizes, including the use of markers and software, as well as the implications of gel quality on accuracy.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • One participant suggests matching the bright spots on the gel to the marker numbers to estimate fragment sizes, seeking confirmation on this approach.
  • Another participant notes that a special formula is needed for precise size determination due to the non-linear migration of DNA, but acknowledges that approximations can be made using the highest and lowest bands.
  • A different viewpoint questions the necessity of a formula, arguing that matching bands to markers suffices unless high precision is required, which would necessitate a higher quality gel for better resolution.
  • One participant requests assistance in determining the number of base pairs for their experiment.
  • Another participant recommends creating an Excel spreadsheet to plot fragment sizes against migration distances, suggesting that a non-linear trendline can be used to estimate sizes based on migration data.
  • A subsequent post reiterates the Excel method for determining fragment sizes, with an agreement from another participant on this approach.

Areas of Agreement / Disagreement

Participants express differing views on the necessity of formulas versus direct matching of bands to markers. While some advocate for the use of software and trendlines for accuracy, others believe simpler methods may suffice depending on the context.

Contextual Notes

Participants mention the impact of gel quality on resolution and the potential need for non-linear modeling, indicating that assumptions about linearity may not hold in all cases.

kevin86
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http://img19.imageshack.us/img19/5510/dnaphysicscg8.jpg

I have the numbers for the marker. So to find out size the fragments I just match the numbers on the markers to the bright spots that I circled right. I just need to double check.
 
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You need a special formula to get the specific size of your band because the migration DNA is not linear. However, you can approximate based on the higher and lower band.

Software that comes with gel documentation/camera can estimate the size for you.
 
Why would you need a formula? Just match the band with that of the marker. Unless you need to know it very precisely, where you'd need a gel that is of a much better quality as the one posted (a higher percentage for instance to get better resolution of the area you are interested in).
 
hey could you help me determine the amount of base pairs for my experiment?
 
Make an excel spreadsheet with two columns. In one column write the size of each DNA fragment, and in the corresponding column write the distance migrated. Make a scatter plot of the fragment size as a function of the distance migrated (or vice-versa) and obtain a non-linear trendline. Use this trendline and the distance migrated by each band to find the fragment size.

This is how we did it in our genetics lab, anyway.
 
Deoxyribose said:
Make an excel spreadsheet with two columns. In one column write the size of each DNA fragment, and in the corresponding column write the distance migrated. Make a scatter plot of the fragment size as a function of the distance migrated (or vice-versa) and obtain a non-linear trendline. Use this trendline and the distance migrated by each band to find the fragment size.

This is how we did it in our genetics lab, anyway.


Agreed! i was gone say the same thing
 

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