Rewriting+Textbooks+on+DNA+Crossover

University of California

 * April 16, 2004**

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The decision to crossover DNA is made much earlier than was previously thought. Evidence shows that this decision is made before pieces of DNA are fully reattached to the chromosome.To better understand this, you will need to know exactly how DNA crossover occurs. DNA crossover occurs during prophase I of meiosis when all of the replicated homologous chromosomes line up together in the nucleus. One side of each of the chromosomes is broken apart and and is then reattached, using the partner chromosone that was not broken as a template. This can result in an exchange of DNA beween the two chromosomes as the broken parts may reattach to the opposite chromosmes. As was stated above, the decision to complete a crossover of DNA occurs earlier than expected. It was previosly thought that this decision happens after the creation of Holliday junction, a type of four way junction where crossover is finalized. Instead, through research done on yeast, it is now known that the decision to crossover genes is made before Holliday junctions are created.======