Figure WN23.7. Repair of double-stranded damage may lead to a somatic crossover, which then causes homozygosity of the region of chromosome distal to the centromere. (A) One of two homologous chromosomes suffers damage (cross). The centromeres are shown at left. (B) At replication, the damage is repaired using information from the homologous chromosome and leads to a crossover. (C) Depending on how the centromeres segregate (arrows in B), the two daughter cells (shown separated by a dotted line here) may become homozygous for the whole region beyond the point of damage. Thus, the gene to the left of the crossover remains heterozygous in both cells (Aa), whereas the gene to the right has become homozygous in both cells (bb, BB).

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