An F factor can pick up the chromosomal DNA, as it exists as a chromosome, which involves the following steps:
• F is inserted in an Hfr strain at the repetitive element, which is identified as the IS (insertion sequence) between the ton and lac+ alleles.
• Then the F factor is inserted.
• Abnormal out looping takes place by crossing over with different elements, IS2, to include the laci locus.
• The resulting F′ lac+ particle is formed.
• Partial diploid of F′ lac+/ F′- lac- is produced by the transfer of the F′ lac+ particle to an F′- lac- recipient.
Thus, the crossover occurring in the orange segments of DNA represent IS elements, which provide homology for crossing over.