TRANSDUCTION

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Hello everyone,. The important methods of genetic transfer are: 1. Transduction 2. Transformation 3. Conjugation. We shall discuss the topic Transduction here. The latter two will be dealt in upcoming blogs. TRANSDUCTION a process of genetic transfer from one microorganism to another. Phages are generally used in this process where in genes are carried from one bacteria to another.[1] History of Transduction: It was in the year 1951 when Joshua Lederberg and Nortan Zinder first carried out the experiments on recombination techniques in Salmonella typhimurium using E.coli as phage. The scientists used two strains: phe? tryp tyr and other was met? his. When a single strain is used and plated on a minimal media, wild type cells were not observed. But when both the strains are used, wild types were observed at a frequency of 1 in 1 lakh. From this the scientists have observed a similar kind of genetic transfer as that of Conjugation which later they termed as Transduction.[1] The principle difference between Transduction and other genetic transfer mechanisms is that the movement of genetic material in transduction is mediated by certain viruses.[2] Types of Transduction: Two types of Transduction process were observed. 1. Generalized transduction 2. Specialized transduction Generalized transduction: [2] In this process, the virus can carry any part of the chromosome. It is a process in which most of the fragments of the bacterial DNA get a chance to enter right into a transducting phage. Virus participating is in lytic phase. Example: Transduction of Coliphage P1: This phage can transduce a variety of genes in the bacterial chromosome. Steps involved in Generalized Transduction: 1. Phage Adsorption on to the host at a particular receptors 2. Penetration of phage DNA into the host cell 3. The phage DNA replicates at the same time the host DNA degrades. 4. Packaging of phage components 5. Lysis of the host cell releasing Transducing phage 6. Transducted genes attacking new host cell. Specialized transduction: [2] Here the transduction process is carried out by phage strains that are capable of transducting only handful of genes. ie., particular portions of the bacterial chromosomes are transducted. Virus participating is in lysogenic phase. Example: Phage Lambda of E.coli Steps involved in Specialized transduction: 1. Phage Adsorption on to the host at a particular receptors 2. The DNA of phage lambda is precisely inserted next to the desired genes (say gal genes-meant for galactose metabolism0 3. The phage lambda is induced, replicated and emerges into normal phage 4. If the excision takes place imperfectly, the gal genes may be removed leading to defective galactose transducing phage. Reference: 1.http://medicine.jrank.org/pages/2885/Transduction-Specialized-Transducti... accessed on 13th March 2011 2.http://www.ncbi.nlm.nih.gov/books/NBK21760/ accessed on 13th March 2011. THIS BLOG DOES NOT CONTAIN PLAGIARIZED MATERIAL
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Author: Sirisha Pingali

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