5. Genetics of Bacteria and Viruses

Transduction

5. Genetics of Bacteria and Viruses

Transduction: Videos & Practice Problems

Topic summary

Transduction is a process where bacteriophages transfer foreign DNA into bacteria, discovered by Lederberg and Zender in 1951. There are two types: generalized transduction, which transfers any bacterial DNA, and specialized transduction, which transfers specific genes near a transducer insertion site. This mechanism allows for gene mapping through cotransduction frequencies, indicating how closely genes are linked. Understanding transduction is crucial for genetic studies and applications in biotechnology, including gene therapy and genetic engineering.

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Transduction

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Transduction Video Summary

Transduction is a fascinating biological process where a bacteriophage, a type of virus that infects bacteria, transfers foreign DNA into a bacterium. This concept was first discovered in 1951 by researchers Lederberg and Zender, who conducted experiments with two mutant strains of E. coli. They mixed these strains and plated them under conditions where neither should survive, yet some cells did grow. This unexpected result indicated that DNA transfer was occurring between the strains.

Initially, the researchers suspected conjugation, a process where bacteria exchange genetic material directly. To test this, they introduced a filter that prevented the physical connection necessary for conjugation. Despite this barrier, the bacteria still grew, leading to the conclusion that a virus, specifically a bacteriophage, was responsible for the DNA transfer. This discovery highlighted the role of bacteriophages in genetic exchange among bacteria.

Transduction can be categorized into two main types: generalized and specialized. Generalized transduction allows for the transfer of any part of a bacterial chromosome. This occurs when a bacteriophage infects a bacterium, causing it to lyse and release fragmented DNA into the environment. The bacteriophage can then incorporate this random DNA and transfer it to another bacterium during subsequent infections.

In contrast, specialized transduction involves the transfer of specific segments of bacterial DNA. This process is mediated by a transducer, a molecule that integrates into a precise location within the bacterial chromosome. When the bacteriophage is activated, it can excise itself along with adjacent genes, which are then packaged into new phages and transferred to other bacteria. This specificity means that only certain genes are consistently transferred, making specialized transduction a targeted method of genetic exchange.

Both types of transduction have significant implications for genetic mapping and studying gene linkage. In generalized transduction, the concept of cotransduction is crucial. Cotransduction occurs when a single bacteriophage carries multiple genes, and the frequency of this event can be used to infer the proximity of genes on a chromosome. The closer two genes are, the higher the likelihood they will be cotransduced together. This relationship allows researchers to map genes based on cotransduction frequencies, providing insights into genetic organization and linkage.

In summary, transduction is a vital mechanism of genetic exchange in bacteria, facilitated by bacteriophages. Understanding both generalized and specialized transduction enhances our knowledge of bacterial genetics and the evolutionary dynamics of microbial populations.

Problem

True or False:Transduction uses viruses to transfer foreign DNA into bacteria

True

False

Problem

Specialized transduction differs from generalized transduction because specialized transduction is defined by what?

The ability to only transfer specific DNA molecules

The ability to transfer any DNA molecules

The ability to transfer DNA and protein

The ability to transfer specific RNA molecules

Problem

A cotransduction experiment was performed with two bacteria strains. The first train has the genotype l+ g m+ while the second strain has the genotype of l g+ m. The researchers found that 46 colonies had cotransduced m+ with l+, while only 25 colonies had cotransduced g with l+. Using this information determine which of the following gene pairs are closest together.

l and m

l and g

m and g

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Here’s what students ask on this topic:

What is transduction in genetics?

Transduction in genetics is a process where bacteriophages, which are viruses that infect bacteria, transfer foreign DNA into a bacterial cell. This mechanism was discovered by Lederberg and Zender in 1951. There are two main types of transduction: generalized and specialized. Generalized transduction can transfer any part of a bacterial chromosome, while specialized transduction transfers only specific genes near a transducer insertion site. This process is crucial for genetic studies and applications in biotechnology, such as gene therapy and genetic engineering.

How was transduction discovered?

Transduction was discovered in 1951 by Joshua Lederberg and Norton Zender. They conducted experiments with two mutant strains of E. coli. When they mixed these strains and plated them on a medium where neither should grow, they observed that some cells survived. To rule out conjugation, they used a filter that blocked cell-to-cell contact but allowed viruses to pass through. The continued growth of some cells indicated that a bacteriophage was transferring DNA between the bacterial cells, leading to the discovery of transduction.

What is the difference between generalized and specialized transduction?

Generalized transduction involves the transfer of any part of a bacterial chromosome. It occurs when a bacteriophage accidentally packages bacterial DNA during the lytic cycle and transfers it to another bacterium. Specialized transduction, on the other hand, transfers only specific genes near a transducer insertion site. This occurs when a bacteriophage integrates its DNA into the bacterial chromosome at a specific site and later excises, taking adjacent bacterial genes with it. This DNA is then transferred to another bacterium during infection.

How can transduction be used to map genes?

Transduction can be used to map genes through a process called cotransduction. In generalized transduction, the closer two genes are on the bacterial chromosome, the more likely they are to be packaged together into a bacteriophage and transferred to another bacterium. By measuring the frequency of cotransduction, scientists can determine the relative distances between genes. Higher cotransduction frequencies indicate that genes are closer together, while lower frequencies suggest they are farther apart. This method helps in studying gene linkage and mapping bacterial genomes.

What are the applications of transduction in biotechnology?

Transduction has several applications in biotechnology. It is used in gene therapy to deliver therapeutic genes into human cells using modified bacteriophages. This method can correct genetic disorders by replacing faulty genes with functional ones. Transduction is also employed in genetic engineering to introduce new genes into bacteria, enabling the production of proteins, enzymes, and other valuable compounds. Additionally, it is used in research to study gene function, regulation, and interactions by transferring specific genes into model organisms.

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