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Genetic Recombination

Genetic Recombination. The acquisition of new genetic information by an organism so that it will differ from its parent. Genetic Recombination in Prokaryotes. Genetic Information in Prokaryotes Can Be Transferred Vertically and Horizontally

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Genetic Recombination

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  1. Genetic Recombination • The acquisition of new genetic information by an organism so that it will differ from its parent

  2. Genetic Recombination in Prokaryotes • Genetic Information in Prokaryotes Can Be Transferred Vertically and Horizontally • Vertical gene transfer (VGT) is the transfer of genetic material from parent cell to daughter cell • Horizontal gene transfer (HGT) is the transfer of DNA from a donor cell to a recipient cell Figure 8.2, page 222

  3. Horizontal Gene Transfer = Genetic Recombination • In prokaryotes, there are 3 ways in which genetic recombination can naturally occur: • Conjugation • Bacterial Transformation • Viral Transduction

  4. Bacterial Conjugation

  5. Conjugation Involves Cell-to-Cell Contact for Horizontal Gene Transfer • In conjugation, a donor cell transfers DNA directly to the recipient • The donor cell forms a conjugation pilus to make contact with the recipient Figure 8.5, page 227

  6. F+ Cells Can Transfer an F+ Plasmid to a Recipient Cell • The F factor DNA in the donor replicates by the rolling-circle mechanism

  7. Conjugation also Can Transfer Chromosomal DNA • High frequency of replication (Hfr) strains can donate chromosomal genes rather than just the F plasmid

  8. Transformation: Griffeth’s Experiment • (See board) • What we learned later • Showed that prokaryotic genome could be “transformed” • The transformation factor

  9. Transformation Is the Uptake and Expression of DNA in a Recipient Cell • By integration of a new DNA fragment, the recipient may have gained some ability it previously lacked • Competence is the ability of a recipient cell to take up DNA from the environment Figure 8.4, page 225

  10. Viral Transduction • Viruses can transfer genes from one cell to another • In order to understand, we must take a look at the viral replication cycles

  11. EM of Bacteriophages

  12. Viral Replication

  13. Lytic CycleLysogenic Cycle

  14. Transduction Involves Viruses as Agents for Horizontal Transfer of DNA • In transduction, a virus (bacteriophage) carries a chromosomal DNA fragment from donor to recipient • In the lytic cycle, virulent phages: • destroy the host chromosome • replicate themselves • destroy the cell • In the lysogenic cycle, temperate phages integrate their DNA into the host chromosome (as a prophage)

  15. Virulent phages perform generalized transduction • A fragment of host cell DNA ends up in the phage during packaging, which they transfer to a new host cell • Temperate phages perform specialized Transduction: In the lysogenic cycle, the prophage eventually excises itself from the host chromosome • Sometimes it takes a few flanking host genes and leaves a few phage genes behind

  16. Viruses Can Cause CancerOncogenes can be transferred during viral transduction

  17. Genetic Engineering and Biotechnology • Genetic Engineering Was Born from Genetic Recombination • Genetic engineering involves changing the genetic material in an organism to alter its traits or products • A recombinant DNA molecule contains DNA fragments spliced together from 2 or more organisms

  18. Genetic Engineering Facility; Ames, Iowa

  19. Genetic Engineering May Offer a New Treatment For Cystic Fibrosis

  20. Specific fragments can be obtained by cutting short stretches of nucleotides with a restriction endonuclease The process creates “sticky ends” The fragments are joined by DNA ligase Figure 8.9, page 236

  21. Genetic Engineering Has Many Commercial and Practical Applications • The genes responsible for producing human insulin can be cloned into bacteria • Bacteria could be genetically engineered to: • break down toxic wastes • produce antibiotics Microinquiry 8, page 239

  22. Plants have been engineered using microbial genes for: • herbicidal activity • viral resistance • Cows produce more milk when injected with bovine growth hormone produced by engineered bacteria Figure 8.11, page 241

  23. “Humulin” is Genetically Engineered Insulin

  24. HGH Has Been Synthesized To Treat Pituitary Dwarfism

  25. Interferon Is Used To Treat Viral Infections and Viral Induced Cancers

  26. Specific nucleotide sequences in pathogens allow us to identify them using DNA probes Figure 8.12, page 242

  27. Recombinant vaccines can be safer than traditional vaccines using killed or attenuated microbes • Heb B vaccine is produced by inserting a Hep. B gene into the yeast genome • Hep B gene produces a surface protein that will be introduced to the patient’s immune system as a “foreign invader” • DNA vaccines are being developed in which a gene serves as the vaccine

  28. Microbial Genomics • Many Microbial Genomes Have Been Sequenced • Hundreds of microbial genomes have been sequenced since the first in 1995 • Many of which are pathogens • Segments of the Human Genome May Have “Microbial Ancestors” • As many as 200 of the 35,000 human genes are essentially identical to those of Bacteria • They were passed down from early ancestors of humans

  29. Microbial Genomics Will Advance Our Understanding of the Microbial World • Knowing genomes of bacteria that cause food-borne diseases can help us: • develop detection methods • make food safer • It can help us identify microbes that cannot be cultured in the lab • Environmental genomics helps us understand how microbial communities function

  30. Microbial Genomics Will Advance Our Understanding of the Microbial World • Environmental genomics can help develop bioremediation techniques • Genomics can help develop detection methods for potential bioweapons organisms and other agents of warfare Figure 8.13, page 246

  31. Comparative Genomics Brings a New Perspective to Defining Infectious Diseases and Studying Evolution • Functional genomics attempts to discover: • the function of proteins coded for in a genome • how the genes interact, allowing the microbe to grow and reproduce • Comparative genomics compares the DNA sequence of one microbe to another similar or dissimilar organism

  32. Some species of bacteria have genomic islands, gene sequences not found in other strains of the same species • Microbiologists learn about pathogenic evolution by comparing pathogenic and nonpathogenic species, or comparing different pathogens • Pathogenicity islands encode many pathogenic characteristics of a species, and are acquired through horizontal gene transfer

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