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crossing over

noun

A process occurring during meiosis wherein two chromosomes pair up and exchange segments of their genetic material.

This occurs at the stage when chromatids of homologous chromosomes pair up during synapsis, forming X-structure (chiasma). The chromatids break into segments (of matching regions), which are then exchanged with one another.

Crossing over is important because it results in new combinations of genes that are different from either parent, contributing to genetic diversity.