Genetic typing of the XL280 congenic pair strains. (A) After 10 backcrosses, both congenic strains XL280α (α) and XL280a (a) contain all of the alleles from XL280p (X) rather than JEC20a (J). The molecular marker segregation indicates that genetic materials from XL280p were transferred to the congenic pairs during backcrosses. DNA regions of the four strains were amplified by PCR, the products were digested with the diagnostic restriction enzyme, and the fragments were resolved on agarose gels. M, Invitrogen 1 Kb+ markers, with a subset of sizes indicated in kilobase pairs. (B) CHEF analyses of chromosomal DNA from the congenic pair strains XL280α (α) and XL280a (a), XL280p (X), and JEC20a (J) indicate identical chromosomal profiles between the congenic pair and XL280p. The MATa donor JEC20a shows a different chromosomal profile.