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http://en.wikipedia.org/wiki/Chromosomal_crossover

It is one of final phases of genetic recombination, which occurs during prophase 1 of meiosis (diplotene) in a process called synapsis.

ologous chromosomes. It is one of final phases of genetic recombination, which occurs during prophase 1 of meiosis (diplotene) in a process called synapsis. Synapsis begins before the synaptonemal complex develops, and is not completed until near the end of prophase 1. Crossover usually occurs when matching regions on matching chromosomes break and then reconnect to the other chromosome.

Crossing over was described, in theory, by Thomas Hunt Morgan. He relied on the discovery of the Belgian Professor Frans Alfons Janssens of the University of Leuven who described the phenomenon in 1909 and had called it 'chiasmatypie'. The term chiasma is linked if not identical to chromosomal crossover. Morgan immediately saw the great importance of Janssens' cytological interpretation of chiasmata to the experimental results of his research on the heredity of Drosophila. The physical basis of crossing over was first demonstrated by Harriet Creighton and Barbara McClintock in 1931.

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Last updated: October 14, 2010