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
- Genetic Cloning
  9m
- Methods for Analyzing DNA
  9m
19. Cancer Genetics29m
- Overview of Cancer
  21m
- Cancer Mutations
  7m
20. Quantitative Genetics1h 26m
21. Population Genetics50m
- Hardy Weinberg
  19m
- Allelic Frequency Changes
  31m
22. Evolutionary Genetics29m

15. Genomes and Genomics

Genomics and Human Medicine

Genetics

15. Genomes and Genomics

Genomics and Human Medicine

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2:27 minutes

Problem 27

Textbook Question

Gene targeting and gene editing are both techniques for removing or modifying a particular gene, each of which can produce the same ultimate goal. What is the main technical difference in how DNA is modified that differs between these approaches?

Verified step by step guidance

Gene targeting involves the use of homologous recombination to introduce specific DNA sequences into a target location in the genome. This process relies on the cell's natural repair mechanisms to incorporate the introduced DNA into the genome.

Gene editing, on the other hand, uses engineered nucleases such as CRISPR-Cas9, TALENs, or ZFNs to create double-strand breaks at specific locations in the genome. These breaks are then repaired by the cell's DNA repair pathways, either through non-homologous end joining (NHEJ) or homology-directed repair (HDR).

In gene targeting, the modification is achieved by providing a DNA template with homologous sequences flanking the target site, which guides the recombination process. This method is less precise and often requires selection markers to identify successful modifications.

Gene editing is more precise because the engineered nucleases are designed to target specific DNA sequences, allowing for targeted modifications without the need for selection markers. The repair process can introduce insertions, deletions, or substitutions depending on the repair pathway used.

The main technical difference is that gene targeting relies on homologous recombination to introduce changes, while gene editing uses site-specific nucleases to create targeted DNA breaks, followed by repair mechanisms to achieve the desired modification.

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Key Concepts

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

Gene Targeting

Gene targeting is a technique that involves the precise alteration of a specific gene within the genome. This is typically achieved through homologous recombination, where a piece of DNA with a desired modification is introduced into a cell, and the cell's natural repair mechanisms incorporate this DNA into the target gene. This method allows for specific changes, such as knockouts or insertions, but can be time-consuming and less efficient.

Gene Editing

Gene editing refers to a broader set of techniques, including CRISPR-Cas9, that allow for the direct modification of DNA sequences at specific locations in the genome. Unlike gene targeting, which relies on homologous recombination, gene editing often uses engineered nucleases to create double-strand breaks in DNA, which the cell then repairs, allowing for insertions, deletions, or substitutions. This method is generally faster and more versatile.

Homologous Recombination vs. Non-Homologous End Joining

Homologous recombination (HR) and non-homologous end joining (NHEJ) are two DNA repair pathways that play crucial roles in gene targeting and editing. HR is a precise repair mechanism that uses a template for accurate modifications, while NHEJ is a quicker, error-prone process that can lead to insertions or deletions at the break site. Understanding these pathways is essential for grasping the technical differences between gene targeting and gene editing.

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Textbook Question

A number of mouse models for human cystic fibrosis (CF) exist. Each of these mouse strains is transgenic and bears a different specific CFTR gene mutation. The mutations are the same as those seen in several varieties of human CF. These transgenic CF mice are being used to study the range of different phenotypes that characterize CF in humans. They are also used as models to test potential CF drugs. Unfortunately, most transgenic mouse CF strains do not show one of the most characteristic symptoms of human CF, that of lung congestion. Can you think of a reason why mouse CF strains do not display this symptom of human CF?

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Textbook Question

When disrupting a mouse gene by knockout, why is it desirable to breed mice until offspring homozygous (−/−) for the knockout target gene are obtained?

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Textbook Question

Craig Venter and others have constructed synthetic copies of viral genomes. For example, the genome for poliovirus and the 1918 influenza strain responsible for the pandemic flu have been assembled this way. The United States currently has a moratorium on federal funding for 'gain-of-function' experiments which increase the virulence or transmission potential of viruses. What concerns might ethicists have about synthetic biology studies involving potential pandemic pathogens?

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Textbook Question

What techniques can scientists use to determine if a particular transgene has been integrated into the genome of an organism?

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Textbook Question

How would you edit a specific nucleotide in a genome?

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Textbook Question

The CRISPR–Cas9 complex directs the Cas9 endonuclease to a specific genomic locus. If the endonuclease domain is inactivated and replaced with a transcriptional activator (or repressor) domain, what would be the functional consequence of directing such a complex to a specific chromosomal location?

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Textbook Question

How might you use CRISPR–Cas9 to create a large deletion?

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Multiple Choice

The human genome project discovered that protein coding regions make up what percent of the human genome?