**Core Concept**
Familial polyposis coli (FPC), also known as Familial Adenomatous Polyposis (FAP), is a genetic disorder characterized by the development of hundreds to thousands of polyps in the colon and rectum. This condition is caused by a mutation in the APC gene, leading to uncontrolled cell growth and increased risk of colorectal cancer.

**Why the Correct Answer is Right**
FAP is an autosomal dominant condition, meaning a single copy of the mutated gene is sufficient to cause the disease. The APC gene normally functions as a tumor suppressor, regulating cell growth and division. Mutations in APC lead to the accumulation of β-catenin, a protein that promotes cell proliferation and inhibits apoptosis. This results in the formation of adenomatous polyps, which can progress to colorectal cancer if left untreated.

**Why Each Wrong Option is Incorrect**
**Option A:** Familial polyposis coli is characterized by the development of polyps in the small intestine, which is incorrect. While polyps can occur in the small intestine, FAP primarily affects the colon and rectum.

**Option B:** The APC gene mutation is responsible for the development of polyps in FAP, which is correct. However, this option is not the incorrect statement we are looking for.

**Option C:** FAP is not caused by a mutation in the TP53 gene, which is a different tumor suppressor gene. While TP53 mutations are associated with Li-Fraumeni syndrome, they are not responsible for FAP.

**Clinical Pearl / High-Yield Fact**
FAP is associated with a high risk of colorectal cancer, with almost 100% of individuals developing cancer by age 40 if left untreated. Regular screening and prophylactic colectomy are essential for early detection and prevention of cancer.

**Correct Answer:** A. Familial polyposis coli is primarily characterized by the development of polyps in the colon and rectum, not the small intestine.