FIG. 1.

Contrasting recombination products from linear homologous DNA versus circular chimeric DNA donors. The top object represents donor DNA; the middle object represents the recipient chromosome; and the bottom object represents the recombinant chromosome. (A) Linear homologous donors cause simple allele replacement within a homologous portion of the resident chromosome; the hatched box of donor DNA with a marker (+) contains a sequence homologous to the open box of the recipient chromosome. + and −, donor and recipient alleles. (B) Circular chimeric donor allows integration of heterologous DNA (cat) between duplicate, recombinant copies of a homologous target sequence; the vertically hatched box of donor DNA is homologous to the horizontally hatched target box of recipient chromosome.