The reciprocal exchange of segments at corresponding positions along pairs of homologous CHROMOSOMES by symmetrical breakage and crosswise rejoining forming cross-over sites (HOLLIDAY JUNCTIONS) that are resolved during CHROMOSOME SEGREGATION. Crossing-over typically occurs during MEIOSIS but it may also occur in the absence of meiosis, for example, with bacterial chromosomes, organelle chromosomes, or somatic cell nuclear chromosomes.
    

concept

Holliday junction and proteins

RuvA protein bound to DNA - side view

The Bar "Gene" a duplication / Calvin B. Bridges.

The effects of unequal crossing over at the bar locus in Drosophila / A.H. Sturtevant.

A correlation of cytological and genetical crossing-over in Zea mays / Harriet B. Creighton and Barbara McClintock.

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Crossing over (Genetics)

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The Bar "Gene" a duplication / Calvin B. Bridges.

Holliday junction and proteins

The effects of unequal crossing over at the bar locus in Drosophila / A.H. Sturtevant.

A correlation of cytological and genetical crossing-over in Zea mays / Harriet B. Creighton and Barbara McClintock.

RuvA protein bound to DNA - side view