DNA extraction techniques for three tissue types. Gel bands, no bands visible? what does this mean?

Question

I'm doing a biology subject at uni and we have just completed our first prac on DNA extraction techniques. There are a few questions that we have to answer for the prac write up and one of those being

:

If no band was visible on the gel for the particular tissue type does this result mean that the DNA extraction was unsuccessful. Explain?

The three tissue types that we extracted dna from were blood, muscle and feather from a domestic chicken. The experiment was run so that we could discover whether the chicken was male or female from the DNA. Can anyone help? i cant find any information on gel bands other than what is in my prac manual.

Thank you =]

Answer 1

Usually when you run gels, you run them with a DNA ladder in the first slot to make sure the gel actually worked.  If you did run a ladder that worked, then most likely your DNA extractions were unsuccessful. Why?  Well the process of extraction can be screwed up pretty easily.  You can use the wrong amount of a certain chemical, or removed the pellet when you were suppose to dispose of the pellet.  Also if the DNA extractions didn't go from a straight extraction to a gel, then they must be stored at

-20 degrees celsius or the DNA will degrade.  Also perhaps the gel wasn't setup correctly.  Hope this helps.

Edit:  Thanks for the extra information.  You don't necessarily need a larger sample size to get more DNA, although that would be ideal.  You can run your DNA sample through PCR a couple of times to amplify it.  I work with Daphnia and trying to get enough DNA from two of the little critters can be pretty difficult, so quite often we run them through several cycles of PCR.

Answer 2

I'm going to make some assumptions here because you haven't provided all the details.

I assume you ran a PCR of some sort (because DNA extractions produce smears, not bands).

Well, a google search says that hens are XY and roosters are XX.

So, based on what you've said, I'm also going to assume the primers you used for your PCR were designed to amplify a region of the Y-chromosome in hens.  Primers designed in this manner should produce no bands in rooster tissues.

So no band does not necessarily mean that your DNA extraction was unsuccessful.  Based on what you've described, it most likely means you were testing DNA that came from a rooster.

There's a separate test to make sure your DNA extraction was successful, but the technique passes my mind right now.

If my assumptions are off, then ignore this message.

Please add more details.

Answer 3

if no bands were visible that could mean a number of things

could have messed up in your proceedure somewhere

i'm guessing you did PCR right? lots can go wrong in PCR

primers, temperature, etc...

maybe you ran the gel for too long and all the DNA moved out the bottom

maybe you connected the diodes wrong and insted the dna going down the gel it went out the top

A LOT can go wrong and this happens often

maybe your method for extraction was either under or over efficient ( destroyed the DNA while extracting)

but im thinking it's something early on because you should have gotten some band or smear or something, not nothing

:/ good luck

Answer 4

Just because you don't see a band doesn't necessarily mean the extraction didn't work.  It depends on your sample size and the efficiency of extraction--you might have DNA present but just not enough to stain well.

Also--genomic DNA extraction should yield very large pieces of DNA, and/or a background of pieces of random sizes.  The very large stuff may not even enter the gel, and the smaller, randomly-sized stuff will just produce a smear, not any distinct band.  See Figure 1 from the link below for what a good genomic extraction from feathers can produce.  The sharp band you see at the top is simply large pieces of DNA which don't enter the gel very far and stack up in that one spot.  Other than that one band, you shouldn't see anything on a gel other than possibly a smear if your DNA is degraded rather than "high quality".

As far as male vs. female--you cannot tell this from a banding pattern.  You'll have to run additional expts, such as trying to amplfiy Y chromosome-specific sequences.