FIG 5.

Recoverable thymidine kinase (TK) revertants created by homologous recombination (HR) from TSCER2 cells. (Left) HR without crossover (noncrossover [NCO]) can produce revertants with or without a loss of heterozygosity (LOH) at exons 4 and 7 (types A to C). When NCO is limited to exon 5, the revertants are non-LOH revertants (type A). When NCO occurs at exon 4 or 7, the revertants show LOH (types B and C). (Right) HR with CO and subsequent mitotic segregation can produce LOH (type F) or non-LOH (type A) revertants. Interallelic crossover (CO) between exons 4 and 5 and the cosegregation of recombinant and nonrecombinant chromatids into the same daughter cell produce homo-LOH from the CO point to the telomere (type F). CO between allelic chromatids and cosegregation of two recombinant chromatids into the same daughter cell generate a non-LOH event because the allelic chromosomes reciprocally exchange alleles at the CO point (type A) (right panel).