Mitotic Recombination leads to cancer?

While crossing over is a normal and essential process during meiosis (the cell division that produces sperm and eggs), its occurrence in mitosis (the process of cell division for growth and repair) can indeed contribute to the development of cancer. Under normal circumstances, mitosis produces two genetically identical daughter cells from a single parent cell. This process is crucial for replacing old or damaged cells and for an organism’s growth. Crossing over, the exchange of genetic material between homologous chromosomes, does not typically happen during mitosis.  However, on rare occasions, a process called mitotic recombination or mitotic crossing over can occur. When this happens in a cell that already carries a heterozygous mutation for a tumor suppressor gene (meaning one healthy copy and one mutated copy of the gene), the consequences can be significant. Loss of Heterozygosity: A Pathway to Cancer Mitotic crossing over can lead to a phenomenon known as loss of heterozygosity (LOH). Here’s a simplified explanation of how this can promote cancer:  1. Initial Mutation: A person may inherit or acquire a mutation in one copy of a tumor suppressor gene. These genes are critical for controlling cell growth and preventing tumors from forming. With one functional copy, the cell can still produce the necessary protein to suppress tumor growth. 2. Mitotic Recombination Event: If mitotic crossing over occurs in a cell with this pre-existing mutation, it can result in a daughter cell that is homozygous for the mutated gene. This means the cell now has two mutated copies of the tumor suppressor gene.  3. Loss of Function: With both copies of the tumor suppressor gene inactivated, the cell loses its ability to control its own growth and division. 4. Uncontrolled Proliferation: This loss of control can lead to unchecked cell proliferation, a hallmark of cancer. The single cell with the homozygous mutation can then divide uncontrollably, forming a tumor.  In essence, mitotic crossing over can be a critical “second hit” in the development of cancer, unmasking a recessive mutation and allowing a cell to become cancerous. Certain genetic conditions, such as Bloom syndrome, are characterized by an increased frequency of mitotic recombination and a significantly higher risk of developing various types of cancer.