**Core Concept**
Loss of heterozygosity (LOH) is a phenomenon where a somatic or germ cell loses one allele of a gene, resulting in the individual being left with only one copy of the gene. This can lead to the expression of a recessive allele, potentially causing disease.

**Why the Correct Answer is Right**
In many cancers, LOH occurs due to the deletion of a chromosomal region containing tumor suppressor genes. This can lead to the inactivation of these genes, allowing unchecked cell growth and tumor formation. For example, LOH of the p53 gene (a tumor suppressor gene) is a common event in various types of cancer. The p53 gene helps regulate cell division and prevents the propagation of cells with damaged DNA.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not directly related to LOH, as it does not involve the loss of one allele of a gene.
* **Option B:** This option is incorrect as it is not a direct consequence of LOH. While genetic mutations can occur during DNA replication, LOH specifically involves the loss of one allele.
* **Option C:** This option is not a direct result of LOH, as it refers to a different genetic mechanism.

**Clinical Pearl / High-Yield Fact**
LOH is often used as a marker for cancer, as it can indicate the presence of a tumor suppressor gene mutation. This is particularly useful in identifying individuals with a higher risk of developing certain cancers.

**Correct Answer: D. Loss of p53 gene**