Kingdom Monera Reproduction - Conjugation
Description:
Conjugation is a type of sexual reproduction which was discovered in E.coli by Lederburg and Tarum in 1946. Bacteria showing conjugation are dimorphic i.e they have two types of cells, male (F+) or donor and female (F-) or recipient.
The male or donor cell possesses 1-4 sex pili on the surface and fertility factor in its plasmid. Fertility factor contains genes for producing sex pili and other characteristics needed for gene transfer.
Gene exchange can occur in two methods −
Sterile male method (F+ X F- → F- becomes F-)
- A plasmid having the fertility factor replicates.
- A copy of the fertility factor gets transferred to the recipient cell through conjugation tube.
- The recipient cell also becomes donor.
- This phenomenon of reversibility of sex is called sexduction.
Fertile Male Method (Hfr X F- → F- remains F-)
The donor cell having fertility factor integrated to its chromosome is called Hfr (high frequency of recombination), meta male or super male because it has a recombination frequency of 1000 times more as compared to normal F+.
Non-integrated F+ plasmids disintegrate in Hfr cells.
Integrated F+ factor breaks the bacterial chromosome at one end of its attachment.
The bacterial chromosome now undergoes replication.
The freed end copy passes into the recipient cell through the conjugation tube.
The fertility factor is rarely transferred as conjugation is maintained for a brief period.
Only a few genes are transferred, one in seven minutes, two in nine minutes, three in ten minutes etc.
Conjugation produces an incompletely diploid zygote known as merozygote or partial zygote.