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Crossing over takes place between the chromatids of two homologous chromosomes. Maternal chromatids are red; paternal chromatids are blue. Lines point to the chiasmata (cross overs)

Crossing over is a basic concept of genetics and cell biology, often called recombination. It occurs during meiosis.

Crossing over involves the exchange of chromosome segments between non-sister chromatids during the production of gametes. The effect is to assort (shuffle) the alleles on parental chromosomes, so that the gametes carry combinations of genes different from either parent. This has the overall effect of increasing the variety of phenotypes present in a population.