Nonrandom transition from asymmetrical to symmetrical hybrid DNA during meiotic recombination

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Abstract
During meiotic recombination, in the b2 gene of Ascobolus immersus hybrid DNA can be formed either on only one (asymmetrical hybrid DNA) or on both (symmetrical hybrid DNA) interacting chromatids. The two phases can be found in the same meiosis, involving the same two interacting chromatids with the symmetrical phase located on the right with regard to the asymmetrical one. We show that the transition from the asymmetrical to the symmetrical phase occurs in a defined region located within the left part of the gene, which is closer to the initiation region. Once formed, the symmetrical hybrid DNA phase seems always to extend to the rightmost mutation sites. This contrasts with asymmetrical hybrid DNA extension, which when it stays in asymmetrical form, may stop within the gene.Key words: Ascobolus immersus, heteroduplex DNA distribution.