Why does crossing not happen in mitosis?

Crossing over doesn't happen during mitosis because the purpose of mitosis is to create identical daughter cells, not to produce genetically different cells.

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During mitosis, a single parent cell replicates its genetic information before dividing into two daughter cells. The daughter cells are identical to each other, and they are identical to the original parent cell. The purpose of mitosis is to produce copies of cells that can create new tissue, usually to...

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During mitosis, a single parent cell replicates its genetic information before dividing into two daughter cells. The daughter cells are identical to each other, and they are identical to the original parent cell. The purpose of mitosis is to produce copies of cells that can create new tissue, usually to replace old or damaged cells (i.e., healing wounds). Mitosis also helps an organism to develop—for example, cell division occurs rapidly during embryogenesis.

Most cells that are replicated are somatic cells that make up your body tissue. However, not all cells in your body are capable of dividing and repairing damage—for example, neurons cannot divide, and neither can the hair cells in your ears. This is why brain damage and hearing loss are permanent if it results from the destruction of these cells.

Genetic recombination—or "crossing over"—occurs during the first phase of meiosis: specifically, during prophase 1. In meiosis, a single parent cell produces four haploid gametes. In other words, meiosis creates four gametes that, by definition, have half the genetic information as a diploid somatic cell. Gametes (sperm and eggs) are used strictly for reproduction, which is why crossing over is necessary—the goal, after fertilization, is to create a genetically unique individual. This is very different from the goal of mitosis.

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