For example, people with the FAP syndrome are born with a variant in the APC gene which makes it behave like a damaged version of the gene. People with damage built-in are at higher risk of cancer because they have a head start on the complete set of damage that is needed to cause cancer. Radiation, chemicals, infections, and other factors can damage genes after birth. Diet is one. Fat, particularly animal fat, raises the risk of colorectal cancer.
Habits are important, too.
Alcohol, tobacco, and lack of exercise all raise the risk. Colorectal cancer can also develop as a complication of other medical conditions, such as ulcerative colitis. All members of a family do not have the same height, weight, and face. Here again, it's genetic and environmental differences that explain differences in our appearance and health. Some family members will inherit genes that predispose to colorectal cancer, and others will not.