Final answer:
CFTR is a symbol for a loss-of-function mutation leading to cystic fibrosis, while a mutated RAS protein is an example of a gain-of-function mutation. Dominant negative mutations, like those in p53, interfere with normal gene function.
Step-by-step explanation:
An example of a loss-of-function mutation is the gene symbol CFTR, which is associated with cystic fibrosis when mutations cause a deletion of three nucleotides resulting in the loss of the amino acid phenylalanine. A gain-of-function mutation can be observed with the RAS protein, where such mutations can lead to an always active oncogene, contributing to the formation of cancer. Dominant negative mutations are a type of gain-of-function mutation that occurs when the mutated gene product interferes with the normal wild-type gene product within the same cell. For example, a mutation in the tumor suppressor gene p53 can result in a dominant negative effect where the defective allele prevents the normal allele from functioning properly.