Entry times of genes depend upon their distance from the entry point of the Hfr Genes are mapped in units of minutes of mating. The gene closest to the inserted F-factor is transferred first Many Hfr strains exist with F inserted in different locations. Any gene can be mapped by using several Hfr strains
• Genes are mapped in units of minutes of mating. • The gene closest to the inserted F-factor is transferred first. • Many Hfr strains exist with F inserted in different locations. • Any gene can be mapped by using several Hfr strains Entry times of genes depend upon their distance from the entry point of the Hfr
F pilus of Hfr cell has established connection with F-cell Hfr cell Fcell Integrated F plasmid Single strand of integrated F plasmid is cut Hfr chromosome F plasmid followed by htr chromosomal replicates itself DNA passes into recipient cell as transfer proceeds Donor dna is replicated in host cell Hfr DNA
Homologous regions on donor Cells separate and recipient DNA Replication Recipient carries part complete of F plasmid and some Donor of Hfr genome plus its DNA own F- genome Recipient DNA Recipient is partly diploid Some of transferred DNa may be incorporated into recipient's (host's chromosome by recombination Cell remains f but carries some genes from hfr chromosome DNA fragments from donor and recipient cells are digested by nucleases Gene transfer in a mating between Hfr donors and F recipients In an Hfr X F mating, single-strand