Definition for Double-strand-break repair model of recombination

Dose-response curve

Double Irony

1) The double strand break model of meiotic recombination allows for unequal amounts of heteroduplex DNA either side of the initial site of recombination, explaining some results that the Meselson-Radding model of recombination does not.

2) The double-strand break model of genetic recombination, in contrast to the Aviemore model, initiates exchanges by a double-strand break and results in two half chiasmas.

Model

The double-strand gap model of recombination was proposed to account for genetic observations in Saccharomyces cerevisiae that could not easily be explained by the Aviemore model. It incorporated observations that double-strand gaps in DNA occur during Meiosis in this Yeast.

In this model a double-strand break (1) initiates the process. The gap is extended by exonuclease action, a 5' exonuclease being more active and exposing 3'-unpaired ends (2). An unpaired 3' end invades the duplex DNA of the homologous chromosome (3) displacing one of the strands. Repair synthesis follows (4), further displacing the previously paired strand. Eventually, the sequence displaced is complementary to the other unpaired 3' end. Repair synthesis follows from the second unpaired 3' end (5).

Interpretations

• This model differs in several important respects from the Aviemore model.
• The model, originally invoked to explain genetic observations in S. cerevisiae, is consistent with many molecular observations regarding recombination in that organism. It is less consistent with observations made studying the genetics of Ascobolus immersus.
• Models are hypotheses constructed to explain observations (facts). Though they are usually a good approximation of what happens, occasionally new information will overturn a model.