DNA extraction techniques are important for molecular biology.
Forensics, biochemistry and molecular biology are all fields of research that routinely need to extract DNA from an organism or a sample. The processes used to do so are called DNA extraction. If you're doing DNA extraction as part of an in-class lab and you find that some students end up with more DNA than others, do not despair -- there are plenty of reasons why this might happen.
Different Sample Size
The amount of DNA you're able to isolate will depend on how much material you start with. If you're working with pieces of fruit like strawberries, for example, some students in the lab might have larger strawberries than others, and hence have more DNA. With bacteria, it might be that some groups had more cells than others. It's entirely possible that some students will wind up with more DNA than others, due to variations in sample size.
Concentration
Adding too much water or buffer when blending up the specimen will make a very dilute solution. You won't be able to see the DNA you extract if the resulting cell soup or homogenate is too dilute. Try repeating the procedure using a less dilute solution. You want to make sure your homogenate is more or less opaque. It's too dilute if it's translucent or transparent.
Temperature
Keep the homogenate cold throughout the procedure. This will improve your yield of DNA. Enzymes called DNAses could chew up some of the DNA at warmer temperatures. High temperatures will denature the DNAses and cause a structural change, but they can also cause the DNA itself to shear and separate. This makes cold temperatures the better option. Some students keeping their DNA cold while others do not could lead to variation in the yield between different groups.
Time
It's important to allow sufficient time for each step. For example, some of the cell and nuclear membranes could remain intact if you introduce the detergent but don't give it long enough to work, and you won't extract all of the DNA. Adding alcohol too fast can cause the alcohol and water to mix rather than forming separate layers, so be especially sure you give this step enough time.
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