Fifty bacterial colonies are on a complete-medium growth plate. The colonies are replica plated to a minimal-medium plate, and 46 colonies grow. What can you say about the bacteria from the four colonies that do not grow? Design an experiment and describe the methods you would use to determine if any of these four colonies are leu⁻, arg⁻, or val⁻.
Table of contents
- 1. Introduction to Genetics51m
- 2. Mendel's Laws of Inheritance3h 37m
- 3. Extensions to Mendelian Inheritance2h 41m
- 4. Genetic Mapping and Linkage2h 28m
- 5. Genetics of Bacteria and Viruses1h 21m
- 6. Chromosomal Variation1h 48m
- 7. DNA and Chromosome Structure56m
- 8. DNA Replication1h 10m
- 9. Mitosis and Meiosis1h 34m
- 10. Transcription1h 0m
- 11. Translation58m
- 12. Gene Regulation in Prokaryotes1h 19m
- 13. Gene Regulation in Eukaryotes44m
- 14. Genetic Control of Development44m
- 15. Genomes and Genomics1h 50m
- 16. Transposable Elements47m
- 17. Mutation, Repair, and Recombination1h 6m
- 18. Molecular Genetic Tools19m
- 19. Cancer Genetics29m
- 20. Quantitative Genetics1h 26m
- 21. Population Genetics50m
- 22. Evolutionary Genetics29m
5. Genetics of Bacteria and Viruses
Working with Microorganisms
Problem 1b
Textbook Question
How do we know that bacteria undergo genetic recombination, allowing the transfer of genes from one organism to another?

1
Understand the concept of genetic recombination in bacteria: Genetic recombination in bacteria involves the exchange of genetic material between different bacterial cells, leading to new combinations of genes. This process can occur through mechanisms such as transformation, conjugation, and transduction.
Examine the evidence for transformation: Frederick Griffith's experiment with Streptococcus pneumoniae demonstrated that non-virulent bacteria could acquire genetic material from heat-killed virulent bacteria, transforming them into virulent forms. This provided early evidence of genetic recombination.
Explore the process of conjugation: Conjugation involves the direct transfer of genetic material between bacterial cells through a physical connection called a pilus. The experiments of Joshua Lederberg and Edward Tatum with E. coli demonstrated that genetic material could be exchanged between bacterial cells, providing further evidence of recombination.
Investigate transduction: Transduction is the process by which bacteriophages (viruses that infect bacteria) transfer genetic material from one bacterial cell to another. The experiments of Norton Zinder and Joshua Lederberg with Salmonella showed that bacteriophages could mediate the transfer of genetic material, confirming another mechanism of recombination.
Summarize the significance of these findings: The combined evidence from transformation, conjugation, and transduction experiments demonstrates that bacteria undergo genetic recombination. These processes allow the transfer of genes between organisms, contributing to genetic diversity and enabling the mapping of bacterial and bacteriophage chromosomes.

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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Genetic Recombination
Genetic recombination is a process where genetic material is exchanged between organisms, leading to new combinations of genes. In bacteria, this can occur through mechanisms such as transformation, transduction, and conjugation. These processes enable bacteria to acquire new traits, enhancing their adaptability and survival.
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Transformation
Transformation is a form of genetic recombination where bacteria take up free DNA from their environment. This DNA can originate from lysed bacterial cells and can integrate into the recipient's genome, allowing for the acquisition of new characteristics, such as antibiotic resistance. This process demonstrates how genetic material can be transferred between organisms without direct contact.
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Transformation
Bacteriophages and Transduction
Bacteriophages, or phages, are viruses that infect bacteria and can facilitate genetic recombination through a process called transduction. During transduction, a phage can accidentally incorporate bacterial DNA into its own genome and transfer it to another bacterium during infection. This mechanism illustrates a significant method of horizontal gene transfer, contributing to genetic diversity in bacterial populations.
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