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Assume a geneticist has transfected embryonic stem cells with a gene-targeting vector containing...

Question:

Assume a geneticist has transfected embryonic stem cells with a gene-targeting vector containing the neomycin resistance gene as a positive selection marker and the thymidine kinase gene as a negative selection marker. She observes that some cells are resistant to neomycin but killed by ganciclovir. What was the outcome of the gene targeting procedure?

A. No recombination.

B. Homologous recombination.

C. Nonhomologous recombination.

D. The transfection did not work.

Transfection:

Scientifically, it is possible to introduce foreign nucleic substances into a cell. The laboratory technique of introducing foreign nucleic substances into a cell is highly used, especially when testing gene manipulation, and is called transfection. The introduced foreign nucleic substance may transiently exist in the cell or may be integrated into the recipient cell's genome. Types of transfection include stable transfection and transient transfection.

Answer and Explanation: 1

Answer: (C) Nonhomologous recombination

Various steps are involved in generating a target vector in a mouse. However, during the various steps involved, the analyst uses a gene marker that helps to demonstrate what is happening in the cell. The obtained results vary depending on the expected outcomes. The outcome of the gene targeting procedure was nonhomologous recombination since some cells were resistant to neomycin but killed by ganciclovir. It indicates random insertion to both the NeoR gene and the TK gene.

Choice (a) is incorrect because some observations were made to some cells, especially in the neomycin, and hence there was some recombination.

Choice (b) is incorrect because homologous recombination occurs in both the right and the left arm of the targeting vector, thus enabling the NeoR gene to replace the target gene segment successfully. During homologous recombination, the resistant cells are not killed in the ganciclovir.

Choice (d) is incorrect because transfection worked and some observable changes to some cells.


Learn more about this topic:

Manipulating Heritable Information
Manipulating Heritable Information

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Chapter 14 / Lesson 14
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In this lesson, we'll be learning different strategies that scientists use to change genetic information in cells and organisms. We'll explore how scientists do this and some common applications.


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