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Chapter 7: Problem 12

As described in Figure 7.10, host DNA is hydrolyzed into small pieces, which are occasionally assembled with phage proteins, creating a phage with bacterial chromosomal DNA. If the breakage of the chromosomal DNA is not random (i.e., it is more likely to break at certain spots as opposed to other spots), how might nonrandom breakage affect cotransduction frequency?

Short Answer

Expert verified
Nonrandom breakage of chromosomal DNA could affect cotransduction frequency by leading to a biased representation of genes in the phage DNA. Genes located near the common breakage points are more likely to be included in the phage DNA and, thus, have a higher cotransduction frequency.

Step by step solution

01

Understand the Phenomenon of Cotransduction

Cotransduction is a molecular genetic method that involves the transfer of genetic material (DNA) from one bacterium to another through a vector known as a bacteriophage. In this process, some of the host bacterial genes can be incorporated in the bacteriophage genome instead of the bacteriophage DNA. These genes can be transferred to another bacterium when the phage infects it.
02

Analyze the Effects of Nonrandom Breakage

If the breakage of chromosomal DNA is not random, meaning it is more likely to break at certain spots as opposed to other spots, then the fragments of DNA that end up in the phage will not be a random sample of the host's genome. Genes located near the points where breakage is more common will be over-represented in the phage population.
03

Evaluate the Impact on Cotransduction Frequency

The nonrandom breakage of DNA would mean that certain genes, specifically those near the common breakage points, are more frequently included in the phage DNA. As a result, the cotransduction frequency of these genes would be higher. In other words, these genes would more commonly be transferred to other cells in the course of phage infection, while genes located further away from the breakage points would be transferred less frequently.
04

Conclusion

In summary, non-random breakage of host DNA results in a biased representation of genetic material in the bacteriophage population. This, in turn, affects cotransduction frequency. Genes near the breakage sites are transferred more frequently than others.

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Most popular questions from this chapter

Antibiotics such as tetracycline, streptomycin, and bacitracin are small organic molecules that are synthesized by particular species of bacteria. Microbiologists have hypothesized that the reason why certain bacteria make antibiotics is to kill other species that occupy the same environment. Bacteria that produce an antibiotic may be able to kill competing species. This provides more resources for the antibiotic-producing bacteria. In addition, bacteria that have the genes necessary for antibiotic biosynthesis contain genes that confer resistance to the same antibiotic. For example, tetracycline is made by the soil bacterium Streptomyces aureofaciens. Besides the genes that are needed to make tetracycline, \(S\). aureofaciens also has genes that confer tetracycline resistance; otherwise, it would kill itself when it makes tetracycline. In recent years, however, many other species of bacteria that do not synthesize tetracycline have acquired the genes that confer tetracycline resistance. For example, certain strains of \(E\). coli carry tetracycline-resistance genes, even though \(E\) coli does not synthesize tetracycline. When these genes were analyzed at the molecular level, it was found that they are evolutionarily related to the genes in \(S\). aureofaciens. This observation indicates that the genes from \(S\). aureofaciens have been transferred to \(E\). coli. A. What form of genetic transfer (i.e., conjugation, transduction, or transformation) is the most likely mechanism of interspecies gene transfer? B. Because \(S\). aureofaciens is a nonpathogenic soil bacterium and E. coli is an enteric bacterium, do you think the genetic transfer was direct, or do you think it may have occurred in multiple steps (i.e., from S. aureofaciens to other bacterial species and then to E. coli)? C. How could the widespread use of antibiotics to treat diseases have contributed to the proliferation of many bacterial species that are resistant to antibiotics?

Describe the steps that occur during bacterial transformation. What is a competent cell? What factors may determine whether a cell will be competent?

Conjugation is sometimes called bacterial mating. Is it a form of sexual reproduction? Explain.

What is cotransduction? What determines the likelihood that two genes will be cotransduced?

What is the role of the origin of transfer during \(\mathrm{F}^{+}\)- and \(\mathrm{Hfr}^{-}\) mediated conjugation? What is the significance of the direction of transfer in Hfr-mediated conjugation?
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