Holliday intermediate

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Holliday intermediate An intermediate structure in genetic recombination, proposed by Robin Holliday in 1964, in which two double-stranded homologous DNA molecules are joined by means of a reciprocal crossover involving one DNA strand of each molecule. It is formed when a single strand of DNA from each chromosome is broken and joined to the other strand at the point of crossover. The region in which strands from different DNA molecules are paired (a heteroduplex DNA sequence) is extended and two strands of the Holliday intermediate are cleaved. The breaks in the DNA sequences are then repaired to form the recombinant products (see illustration).