---
title: "Gene Targeting | General Biology I"
description: "Gene targeting is the precise alteration of a chosen gene using homologous recombination, a core biotechnology method in General Biology I."
canonical: "https://fiveable.me/college-bio/key-terms/gene-targeting"
type: "key-term"
subject: "General Biology I"
unit: "Unit 17"
---

# Gene Targeting | General Biology I

## Definition

Gene targeting is a biotechnology method that changes a specific gene by using homologous recombination to insert, delete, or replace DNA at one chosen spot. In General Biology I, it shows how scientists edit genomes with precision.

## What It Is

Gene targeting is a way to make a planned change in one specific gene in a genome. In General Biology I, you usually see it as a biotechnology technique that lets scientists delete a gene, replace it with a modified version, or insert a new sequence at a chosen location.

The core idea is to use homologous recombination, which is the cell's natural ability to swap DNA segments that share matching sequence. A targeting vector is built with DNA that matches the region around the gene you want to change. Because the vector contains matching ends, the cell can line it up with the chromosome and exchange the engineered DNA for the original version.

That precision is what makes gene targeting different from random DNA insertion. Instead of adding foreign DNA anywhere in the genome, the change is aimed at one locus. Scientists often include a selectable marker in the targeting vector, such as an antibiotic resistance gene, so they can identify cells that actually took up the engineered DNA and completed recombination.

Gene targeting became especially famous in research with knockout mice. In a knockout, a gene is disrupted so it no longer works, which lets researchers ask what happens when that gene is missing. If the mouse shows a change in development, metabolism, behavior, or disease susceptibility, that gives clues about the gene's normal function.

Modern gene targeting often uses CRISPR/Cas9 to make the process more efficient. CRISPR/Cas9 cuts the DNA at a chosen site, creating a double-strand break. The cell then repairs that break, and researchers can supply a DNA template so the repair machinery uses the desired sequence. In other words, gene targeting still depends on the cell's own repair systems, but CRISPR makes it much easier to get the cut exactly where you want it.

A common way to picture it is this: homologous recombination is the swap mechanism, the targeting vector is the replacement piece, and the selectable marker is the screening tag that tells you which cells likely got the edit. The result is a genome change that can be studied, tracked, and sometimes used in therapy research.

## Why It Matters

Gene targeting shows how biotechnology moves from reading DNA to changing DNA on purpose. In General Biology I, that matters because a lot of genetics is about connecting genotype to phenotype, and gene targeting gives you a direct way to test that connection.

It also ties together several big course ideas at once: DNA structure, mutation, DNA repair, and inheritance. If a gene is knocked out and a trait changes, you have a cause-and-effect link that is stronger than just noticing correlation. That makes gene targeting a powerful research tool for figuring out what a gene actually does in a cell or organism.

The technique also comes up whenever the class talks about modern genetic engineering. It is one of the clearest examples of how scientists can use cell machinery, especially homologous recombination and DNA repair, to make precise changes instead of random ones. That difference is central in biotechnology units because it explains why some methods are better for editing, while others are better for cloning or screening.

Gene targeting also connects to medicine and ethics. The same logic used to study knockout mice can be extended toward gene therapy research, where the goal is to correct or replace harmful sequences. That raises questions about safety, off-target effects, and when changing DNA in cells or embryos should be allowed.

## Connections

### Homologous Recombination

Gene targeting depends on homologous recombination because the cell has to recognize the matching DNA arms on the targeting vector and the chromosome. Without that sequence similarity, the engineered DNA is much less likely to land in the correct place. If you understand this process, gene targeting makes a lot more sense as a controlled swap instead of a random insertion.

### CRISPR/Cas9

CRISPR/Cas9 often boosts gene targeting by cutting the DNA at a chosen site first. That double-strand break gives the cell a strong reason to repair the region, which makes it easier to insert the new DNA template. In class problems, CRISPR usually shows up as the tool that improves targeting efficiency, not the target itself.

### Knockout Mouse

A knockout mouse is one of the most common outcomes of gene targeting in research. Scientists disable a gene in the mouse genome and then observe what changes in the organism. That lets you connect one gene to one function, which is a major goal in functional genomics.

### [Gene therapy](/college-bio/key-terms/gene-therapy)

Gene targeting and gene therapy overlap because both involve making a genetic change with a purpose. Gene targeting is usually the research method or engineering strategy, while gene therapy focuses on treating disease by correcting or adding DNA in patient cells. The same precision that helps build knockout models also points toward therapeutic editing.

## On the AP Exam

A quiz or lab question on gene targeting usually asks you to trace the steps of the technique, not just name it. You might need to identify why homologous recombination matters, predict what a selectable marker does, or explain why a double-strand break from CRISPR/Cas9 improves editing efficiency.

If you get a diagram, look for the matching DNA arms, the modified gene region, and the place where the edit replaces or disrupts the original sequence. If the question describes a knockout mouse, connect the phenotype back to the targeted gene and explain how that mutation helps reveal gene function.

For short answers, the best move is to describe the before and after, original gene, engineered DNA, recombination event, and resulting change in expression or function. That shows you understand gene targeting as a mechanism, not just a vocabulary word.

## Gene targeting vs CRISPR/Cas9

People often mix these up, but they are not the same thing. CRISPR/Cas9 is the genome-editing tool that cuts DNA at a chosen site, while gene targeting is the broader strategy of making a specific planned change in a gene, often by using homologous recombination after the cut.

## Key Takeaways

- Gene targeting is the precise alteration of one chosen gene in a genome, usually by using homologous recombination.
- It can create mutations, deletions, or replacements, so the final DNA sequence is changed in a controlled way.
- Selectable markers help scientists identify cells that successfully incorporated the targeting vector.
- Knockout mice are a classic application because they let researchers connect a gene to a trait or disease process.
- CRISPR/Cas9 often improves gene targeting by making a break at the exact site where the edit should happen.

## FAQs

### What is gene targeting in General Biology I?

Gene targeting is a biotechnology method for changing one specific gene at a chosen spot in the genome. It usually works by using homologous recombination so the cell swaps in an engineered DNA sequence instead of the original one. In biology classes, it shows up as a way to study gene function and make knockout organisms.

### How is gene targeting different from CRISPR/Cas9?

CRISPR/Cas9 is a tool that cuts DNA at a specific location, while gene targeting is the overall strategy of making a planned change to a gene. CRISPR often helps gene targeting work better because the cut encourages the cell to repair the site using the DNA template you provide. So CRISPR is often part of the method, but it is not the same thing as the whole process.

### Why do scientists use selectable markers in gene targeting?

Selectable markers let scientists find the cells that successfully took up the targeting vector and underwent recombination. A common example is an antibiotic resistance marker, which makes only edited cells survive under selective conditions. That way, researchers do not have to guess which cells got the correct DNA change.

### How does gene targeting relate to knockout mice?

Knockout mice are often made with gene targeting by disrupting a gene so it no longer works. Researchers then study the mouse's phenotype to see what changes when that gene is missing. This is a direct way to test gene function in an animal model.

## Related Study Guides

- [17.1 Biotechnology](/college-bio/unit-17/1-biotechnology/study-guide/Kw1lhg3kIiGoGZv7)

## About This Document

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