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Mitotic Recombination: Why? When? How? Where?

Figure 1

Reciprocal crossovers and gene conversion.

(A) An RCO is depicted between chromatids of two homologous chromosomes. One segregation pattern results in daughter cells that have become homozygous for the sequence distal to the crossover site. (B–D) A close-up view of the region outlined by the dotted box, showing different gene conversion tract configurations detectable using markers a through d. (B) No conversion tract, either because there was no gene conversion or the tract was too small to be detected with the markers available. All markers are still present in a 2∶2 ratio. (C) A typical gene conversion event produces a tract that alters some of the markers (b and c) to a 3∶1 ratio. Note that conversion tracts can only be detected if both reciprocal products (i.e., both daughter cells) are recovered and analyzed, as done by Lee et al. (D) Lee et al. observed some tracts that were wholly or partially 4∶0. In the example shown here, marker b has segregated 4∶0, but marker c has segregated 3∶1; this is therefore a 4∶0/3∶1 hybrid gene conversion tract.

Figure 1