Transfer of genetic material by bacteriophage is -
Ans. is 'a' i.e., Transduction Transduction* The transfer of a portion of DNA from one bacterium to another by a bacteriophage (virus).* Bacteriophages are viruses that parasite bacteria and consist of nucleic acid core and a protein coat.* Transduction may be1. Generalised - When it involves any segment of donor DNA2. Restricted - When a specific bacteriophage transduces only a particular genetic trait eg. prophage lambda in E coli K 12 (Gal +gene - Determines fermentation of galactose)* Transduction is not confined to transfer of chromosomal DNA, episomes and plasmid may also be transduced.* The plasmid determining penicillin resistance in staphylococci are transferred from cell to cell by transduction.* Transduction appears to be the most widespread mechanism of gene transfer among prokaryotes.* Transduction is an excellent tool for the genetic mapping of bacteria.* Transduction has been proposed as a method of genetic engineering in the treatment of some inborn errors of metabolism.Lysogenic conversion* In lysogenic conversion the phage DNA itself is the new genetic element as it becomes integrated with the bacterial host DNA with which it multiplies and is transferred to daughter cells, e.g. diptheriae corynebacterium.T ransformation* This is the transfer of genetic material through the agency of free DNA (May involve taking up of soluble DNA with host DNA and codes new species through the cell wall).* Transformation was the first example of genetic exchange (horizontal gene transfer) in bacteria to have been discovered.* It was demonstrated in Streptococcus pneumoniae by Griffith in 1928.* Other organisms in which transformation has been studied are Bacillus, Haemophilus and BPH.Conjugation* Bacterial conjugation is the transfer of genetic material between bacteria through direct cell to cell contact or through a bridge- like connection between two cells.* Conjugation is process where by a donor (male) bacterium makes physical contact with a recipient (female) bacterium.* Donor status is determined by the presence of plasmid.* This plasmid codes for specialized fimbria (sex pilus) and for self transfer.* Sex pilus (conjugation tube) helps in transfer of genetic material from male bacterium to female bacterium.* The plasmid is known as transfer factor (sex factor or fertility factor).* Plasmid may be Rfactor, which codes for transferable multiple drug resistance.* The DNA of the plasmid replicates during transfer so that each bacterium receives a copy - Recipient becomes donor and the donor retains its donor status.SummaryGene transfer in bacteriaa) Transformation-Transfer of genetic material through the agency of free DNA (may involve taking up soluble DNA fragments across their cell wall from other species).b) Transduction-Transfer of a portion ofDNA by bacteriophage (a virus).c) Conjugation-Transfer of genetic material by physical contact.d) Lysogenic conversion-Incorporation of phage DNA into host DNA.
Transduction
Transformation
Transcription
Integration
General