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Ch. 8 - Genetic Analysis and Mapping in Bacteria and Bacteriophages
Klug - Essentials of Genetics 10th Edition
Klug10th EditionEssentials of GeneticsISBN: 9780135588789Not the one you use?Change textbook
All textbooksKlug 10th EditionCh. 8 - Genetic Analysis and Mapping in Bacteria and BacteriophagesProblem 4b
Chapter 8, Problem 4b

With respect to F⁺ and F⁻ bacterial matings, answer the following questions: How was it established that chromosome transfer was unidirectional?

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1
Understand the biological context: In bacterial conjugation between F⁺ (donor) and F⁻ (recipient) cells, genetic material is transferred from one cell to another. The question focuses on how it was shown that this transfer occurs in one direction only—from the F⁺ donor to the F⁻ recipient.
Review the experimental design: Scientists mixed F⁺ and F⁻ bacteria and then separated the two populations after conjugation. They used genetic markers unique to each strain to track the movement of DNA.
Analyze the results: By checking which markers appeared in the recipient cells after mating, researchers observed that only donor markers were transferred to the recipient, and no recipient markers were found in the donor cells.
Interpret the findings: The absence of recipient markers in donor cells indicated that DNA transfer did not occur from F⁻ to F⁺ cells, establishing the unidirectional nature of chromosome transfer during conjugation.
Summarize the conclusion: The unidirectionality was confirmed by the selective presence of donor genetic material in recipients and the lack of reciprocal transfer, demonstrating that chromosome transfer proceeds only from F⁺ to F⁻ cells.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

F⁺ and F⁻ Bacterial Mating

F⁺ bacteria contain the fertility factor (F plasmid) and can initiate conjugation by forming a pilus to connect with F⁻ bacteria, which lack the F plasmid. This mating allows genetic material transfer from F⁺ to F⁻ cells, enabling the study of gene transfer mechanisms.
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F Factor and Hfr

Unidirectional Chromosome Transfer

In bacterial conjugation, DNA transfer occurs only from the F⁺ donor to the F⁻ recipient, not in reverse. This unidirectionality was demonstrated by tracking genetic markers and observing that only the recipient acquired donor genes, confirming the direction of transfer.
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Chromosome Structure

Use of Genetic Markers to Trace DNA Transfer

Researchers used specific genetic markers on donor and recipient chromosomes to monitor gene movement during conjugation. By analyzing which markers appeared in the recipient after mating, they established the direction and extent of chromosome transfer.
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Mapping with Markers
Related Practice
Textbook Question

Write a short summary that contrasts how recombination occurs in bacteria and bacteriophages.

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Textbook Question

With respect to F⁺ and F⁻ bacterial matings, answer the following questions: How was it established that physical contact between cells was necessary?

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Textbook Question

With respect to F⁺ and F⁻ bacterial matings, answer the following questions: What is the genetic basis for a bacterium's being F⁺.

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Textbook Question

List all major differences between:

(a) The F⁺ x F⁻ and the Hfr x F⁻ bacterial crosses

(b) The F⁺, F⁻, Hfr, and F' bacteria.

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Textbook Question

Describe the basis for chromosome mapping in the Hfr x F⁻ crosses.

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