Describe one of the main challenges in extracting dna from cells found at a crime scene.

There can be many challenges while collecting DNA from the cells that is found at the crime scene.

One of the main problem is the minute amount or less amount of DNA that is found at the time of crime scene. this small amount is not sufficient for the reactions that is carried out.

Even PCR needs a detectable amount of DNA for the reactions to take place. The DNA that is found is contaminated most of the time. It is made of protein which gets denatured and then it becomes useless.

the answer to your question is sperm