Explain how a mutation in the DNA sequence of a gene can cause that person to
become sick.

DNA mutations cause cancer or an inability for proper function of the immune system.

Explanation:

DNA is our blueprint, so if something is wrong on the blueprint, then our body will "collapse" like a building (well not always).  Let's say, the gene for immune system function is mutated and comes out wrong. That person might not be able to make white blood cells which fight off sickness. Other mutations can also cause cancer, which is a really bad form of sickness.

cancer   is   essentially   uncontrolled   mitosis   of specialized cells