Horizontal Gene Transfer

Start by watching the video below. Then complete the flashcards and quizzes. For a deeper dive into this material, complete this tutorial in our AP Bio 2.0 Curriculum: Topic 6.7 Part 5: Horizontal Gene Transfer

1. Watch this video

2. Study this summary

Horizontal vs. Vertical Gene Transfer

  • Vertical Gene Transfer:
    • Parents transmit all or half of their genome to their offspring.
    • Examples:
      • A bacterium reproducing, transmitting its entire genome to the next generation.
      • Humans passing on their genes to their offspring through their gametes.
  • Horizontal Gene Transfer:
    • Genes are transferred between organisms that are not offspring.
    • In unicellular organisms, newly acquired genes are integrated into the genome and passed to offspring during reproduction.
    • In multicellular organisms, genes must be transferred into the germline to produce intergenerational effects.

Mechanisms of Horizontal Gene Transfer

  1. Bacterial Conjugation:
    • A process where bacteria transfer plasmids (small loops of DNA) to another cell.
    • Steps:
      • Plasmid genes express a membrane extension called a pilus.
      • The pilus contacts a recipient cell, and the plasmid is copied and transmitted through the pilus.
    • Key Role:
      • Spreads antibiotic-resistant genes through bacterial populations.
  2. Bacterial Transformation:
    • Bacteria pick up DNA fragments from the environment.
    • DNA fragments or plasmids are incorporated into the bacterial genome.
    • Application:
      • Used in genetic engineering to introduce foreign genes (e.g., human genes) into bacterial cells via genetically engineered plasmids.
  3. Viral Transduction:
    • Horizontal gene transfer facilitated by viruses.
    • Process:
      • During viral infection, the virus breaks apart the host’s genome.
      • Errors during viral replication can cause the host cell’s DNA fragments to be incorporated into new viral particles.
      • When the virus infects a new host, it transfers the previous host’s DNA, which recombines with the new host’s DNA.
    • Implication for multicellular eukaryotes:
      • If germline cells experience viral infection followed by viral transduction, new genes may become part of the recipient species’ gene pool.
  4. Viral Recombination:
    • Occurs when two different viruses infect the same host cell.
    • Process:
      • DNA from the two viruses mixes, leading to the emergence of new viral strains.
    • Example:
      • Pandemic flu outbreaks result from this process, as immune systems fail to recognize novel viral strains.

Importance of Horizontal Gene Transfer

  • Enables genetic diversity and rapid adaptation in microbial populations.
  • Plays a significant role in the spread of traits like antibiotic resistance.
  • Drives evolution by introducing new genes across species boundaries.

3. Master these flashcards

[qdeck style=”width: 600px !important; min-height: 450px !important;” bold_text=”false” qrecord_id=”sciencemusicvideosMeister1961-Horizontal Gene Transfer, APBVP”]

[h] Horizontal Gene Transfer Flashcards

[i]

[start]

[q json=”true” yy=”4″ unit=”6.Gene_Expression_and_Regulation” dataset_id=”AP_Bio_Flashcards_2022|177d4fdc05110″ question_number=”259″ topic=”6.7.Mutation”] Contrast “vertical gene transfer” with “horizontal gene transfer.”

[a] In vertical gene transfer, parents transmit all or half of their genome to their offspring (depending on whether reproduction is asexual or sexual, respectively).

In horizontal gene transfer, one organism transfers genes to another organism that is not its offspring. If the recipient is unicellular, then these newly acquired genes become part of the recipient’s genome, and will then get passed to its offspring. In a multicellular organism, horizontal transfer only has long-lasting results if the genes are transferred into the germline (the cells that create an egg or sperm cells).

[q]What happens to acquired genes in unicellular organisms during horizontal gene transfer?
[a]Through recombination, newly acquired genes are integrated into the genome and passed to offspring during reproduction.

[q]What must happen for horizontal gene transfer to have intergenerational effects in multicellular organisms?
[a]The genes must be transferred into the germline.

[q json=”true” yy=”4″ unit=”6.Gene_Expression_and_Regulation” dataset_id=”AP_Bio_Flashcards_2022|1773ffac75110″ question_number=”262″ topic=”6.7.Mutation”] Describe bacterial conjugation.

[a] Bacteria have, in addition to their main chromosome, small circles of DNA called plasmids (b). These plasmids can be copied in one bacterial cell, with the copy transmitted to a second bacterial cell via a membrane extension called a pilus (c). This transfer of plasmids transfers whatever genes are encoded on the plasmid to the second cell, which can, in turn, transmit this plasmid to another bacterial cell (or its offspring).

[q json=”true” yy=”4″ unit=”6.Gene_Expression_and_Regulation” topic=”6.7.Mutation” dataset_id=”AP_Bio_Flashcards_2022|128360de709c14″ question_number=”263″] Describe bacterial transformation.

[a] In bacterial transformation, bacteria pick up DNA fragments (a) from the environment, which become incorporated into the genome (c). In genetic engineering, small loops of DNA called plasmids can be forced into bacterial cells, and this forced uptake of plasmids is also referred to as transformation.

[q json=”true” yy=”4″ unit=”6.Gene_Expression_and_Regulation” dataset_id=”AP_Bio_Flashcards_2022|176aaf7ce5110″ question_number=”264″ topic=”6.7.Mutation”] Describe how horizontal gene transfer can occur through viral transduction.

[a]

Transduction is a type of horizontal gene transfer that can occur through viruses. During viral infections, the virus breaks apart the host’s genome. Sometimes, DNA fragments from the host are mistakenly incorporated into a virus. As a result, when that virus infects a cell in another organism, it can bring in that other organism’s DNA. If the virus infects a germ-line cell, then new genes can be incorporated into the gene pool of the recipient.

[q]What is the significance of bacterial conjugation to public health.
[a]Bacterial conjugation plays a key role in spreading antibiotic-resistant genes through bacterial populations, diminishing the effectiveness of antibiotics.

[q]What is viral recombination?
[a]A process where two different viruses infect the same host cell, and their DNA mixes, creating new viral strains.Viral recombination can lead to the emergence of novel viral strains, such as new flu strains, which can cause pandemics.

[q]How does horizontal gene transfer drive evolution?
[a]It introduces new genes across species boundaries, enabling genetic diversity and rapid adaptation.

[q]Why is horizontal gene transfer important in microbial populations?
[a]Processes like conjugation and tranformation can spread genes for beneficial traits like antibiotic resistance, enhancing survival and adaptation.

[/qdeck]

 

4. Tackle this quiz

[qwiz random=”true” qrecord_id=”sciencemusicvideosMeister1961-Conjugation and Transformation, APBVP”]

[h] Horizontal Gene Transfer

[i]

[q] When you inherited genes from your parents, that was an example of [hangman] gene transfer. When one bacterial cell takes up and integrates genes from another bacterial cell, that’s an example of [hangman] gene transfer.

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[q] In the diagram below, the structure at “c” is called a [hangman]. It’s used to transfer a [hangman] (at “b”) from one cell to another. This type of horizontal gene transfer is called [hangman].

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[q] The process shown below is called [hangman]. It occurs when a bacterial cell absorbs DNA from its [hangman].

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[q] In the diagram below, newly integrated genes are shown at

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[f]IE5vLiBIZXJlJiM4MjE3O3MgYSBoaW50LiBOb3RlIHRoZSBjb2xvciBjb2RpbmcgdXNlZCB0byByZXByZXNlbnQgdGhlIEROQSBpbiB0aGUgZGVhZCBjZWxsIChBKSwgYW5kIHRoZSBETkEgaW4gdGhlIGxpdmluZyBjZWxsIG5lYXJieS4=[Qq]

[q] In the diagram below, the transformed cell is shown

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[q] In the diagram below, a plasmid is at letter

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[q] In the diagram below, a phage that has picked up the “wrong” genetic material is shown at

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[c]ICo=[Qq]

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[q] In the diagram below, the new DNA that has been introduced into bacterial cell 2 is indicated by

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[c]ICo=[Qq]

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[q]The process below represents [hangman]. This is a form of [hangman] gene transfer in which a phage mistakenly incorporates [hangman] from one cell and transmits it to another cell.

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[q] In the diagram below, conjugation is represented by

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[c]ICo=[Qq]

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[q] In the diagram below, transformation  is represented by

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[c]ICo=[Qq]

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[q] In the diagram below, transduction  is represented by

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[q] In the diagram below, vertical gene transfer is represented by

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[q]In the diagram below, “A” represents [hangman], “B” represents [hangman], and “C” represents [hangman]. All of these are forms of [hangman] gene transfer.

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[/qwiz]

 

What’s Next?

Please proceed to our next tutorial: Biotechnology/Genetic Engineering