Experiment: Agarose Gel Electrophoresis of DNA Fragments
- List the distances traveled in mm for the bands in the DNA ladder in the table below.
Remember, smaller fragments travel farther than longer ones, so the top-most band will be the 1,000 bp sized DNA fragments whereas the bottom-most band will be the 50 bp sized DNA fragments.
DNA Ladder Band Distance (mm) 50 bp 90 mm 100 bp 77 mm 150 bp 69 mm 200 bp 64 mm 250 bp 60 mm 300 bp 56 mm 400 bp 51 mm 500 bp 47 mm 600 bp 43 mm 700 bp 40 mm 800 bp 38 mm 900 bp 36 mm 1,000 bp 34 mm
- Whose sample had the approximately 570 bp and 320 bp sized DNA fragments?
- What were the sizes of the DNA fragments for alleged father #1?
41 mm 670bp
43 mm 600bp
- Which size DNA fragment did the child inherit from her mother?
37 mm 850bp
- Which alleged father, if any, can be definitively ruled out as the child’s biological father?
- How are new molecules of DNA synthesized in living cells?
- What is the function of DNA?
DNA has genetic information that controls our cells. So, DNA is like a blueprint that shows how to construct components of cells like proteins and ribonucleic acid (RNA). This information is carried down to newer generations through inheritance.
- If each individual has such a small amount of DNA in their cells, how do the bands on the gel contain enough DNA to be visible?
In order to make DNA visible. The Gel has to be soaked in a dye (ethidium bromide) to bind with the DNA and rinsed off after. Ethidium bromide helps to make DNA visible by glowing brightly in UV rays.
- Humans only have a few eye colors and only four ABO-based blood types. How can DNA tests definitively identify individuals when many people have brown eyes or type A blood?
- Suppose a suspicious hair was found in a victim’s home. A gel is set up with the DNA fragments of two suspected criminals in lanes 4 and 5, the DNA fragments of the suspicious hair in lane 3, and the victim’s DNA fragments, as a negative control, are in lane 2. A DNA ladder is in lane 1. The resulting gel is below. Which suspect, if any, committed the crime? Explain your answer.