Biology Forums - Study Force

Hi guys.. I hope you could enlighten me a bit

Is there a method these days for searching a specific DNA in large quantities of material?
Let's say, finding urine traces of a specific person in a small pool or a large pile of sand?


tnx!

Even if you do find urine, you won't be able to trace any DNA because urine typically doesn't contain cells or any genetic material. That is, unless the person has a medical condition where they urinate blood. The kidney filters out the blood so that only water (including ions, minerals) is excreted.

Nice to know... Although while searching around the internet I could find a lot of people claiming urine DOES contain DNA. How likely is it that urine won't practically contain any DNA?

Also, is it the same with feces?

I think he's right, urine doesn't contain DNA - or it shouldn't. It may contain epithelial cells, which do contain DNA, but this wouldn't be released into urine unless you're sick. Most healthy individuals, however, do not excrete epithelial cells in their urine. Feces is made up of proteins, waste products, and fat from your diet. Technically, you should find DNA from dead cells inside of your digestion system that are excreted as well, but you'd also find cells (DNA) from the things you ingested (the food you ate).

So if it is that hard to extract DNA from urine and feces, I assume it's right next to impossible if it's mixed and scattered in another matter. Is that correct?

Nevertheless, I'm interested what techniques (if any) is there for finding human cells in large quantities of water/sand/etc. Moreover, is there a way to efficiently find cells containing a specific DNA?

You mean like, if the DNA belongs to a human or to a cat, for example. If so, Yes! Specific sequences are found in specific animals, so when you do test a sample of cells, you test it using a concoction of different DNA marker to see which animal it belongs to. However, because all animals, including us, have a similar origin, it's difficult to decipher between closely related animals and the genome of all animals haven't all been sequenced.


Yes, because DNA gets damaged quite easily.

even marked as "solved", I have to write this:I dont know where you get this nonsense that urine doesnt contain DNA. You can DNA profile a person based on urine sample! Although it contains much less DNA molecules (compared to e.g. blood) and urea can be a potent PCR inhibitor. It is also not true that DNA in urine is just in pathological cases.

I sort of agree with Howard. Why would urine contain DNA? If it does, you know the person likely has damaged kidneys.

@duddy: it does contain even in healthy individuals (without damaged kidneys)! I am sorry but you are wrong. With no offence, if you are not a DNA expert, please do some research first and then give answers. Speculation (guessing) is not equal to fact.
Urine is not as good as other body fluids for DNA analysis (1ml of blood can contain 1000-40000 times more DNA compared to 1ml urine), but it can be used. Normally a fresh urine is a good candidate for DNA analysis, crime scene urine - it depends (it is affected by environmetal factors, time). Urine samples taken from crime scene (if you find it) can be quite challenging and will probably give you only mtDNA (but not always, sometimes you can get nuclear DNA profile as well or in another case just nothing).