Genetic Engineering for IGCSE Biology | IGCSE 生物：基因工程考点精讲

📚 Genetic Engineering for IGCSE Biology | IGCSE 生物：基因工程考点精讲

Genetic engineering is a powerful biotechnology that allows scientists to alter the DNA of an organism, introducing new traits or modifying existing ones. In IGCSE Biology, you need to understand how genes are transferred between species, the enzymes involved, and the real-world applications such as insulin production and genetically modified crops. This article breaks down every key point in simple steps, helping you master both the processes and the ethical debates.

基因工程是一种强大的生物技术，使科学家能够改变生物体的DNA，引入新性状或修改现有性状。在IGCSE 生物学中，你需要理解基因如何在不同物种间转移，所涉及的酶，以及实际应用，如胰岛素生产和转基因作物。本文逐步拆解每一个重点，帮助你掌握流程和伦理讨论。

1. What is Genetic Engineering? | 什么是基因工程？

Genetic engineering, also known as genetic modification, involves changing the genetic material of an organism by removing, inserting, or altering individual genes. The aim is to give an organism a desirable characteristic that it does not naturally possess. This is achieved by transferring a gene from one organism into another, creating recombinant DNA.

基因工程，也称基因修饰，是通过移除、插入或改变个别基因来改造生物体的遗传物质。其目的是赋予生物体一种它本来不具备的理想特性。这通过将一个生物的基因转移到另一个生物中，形成重组DNA来实现。

2. Key Enzymes and Tools | 关键酶与工具

Two main enzymes are essential for genetic engineering: restriction enzymes (also known as restriction endonucleases) cut DNA at specific recognition sequences, leaving sticky ends; DNA ligase joins the sugar-phosphate backbones of DNA fragments to seal the gene of interest into a vector.

基因工程中两种主要的酶不可或缺：限制酶（也称限制性内切酶）在特定的识别序列处切割DNA，留下黏性末端；DNA连接酶将DNA片段的糖-磷酸骨架连接起来，把目标基因封接到载体中。

Vectors, usually bacterial plasmids or viruses, carry the foreign gene into a host cell. The plasmid must have an origin of replication and a marker gene, such as antibiotic resistance, to identify successfully transformed cells.

载体，通常是细菌质粒或病毒，将外源基因带入宿主细胞。质粒必须含有复制起点和标记基因，如抗生素抗性基因，以识别成功转化的细胞。

3. Steps of Genetic Engineering Using Bacterial Plasmids | 利用细菌质粒进行基因工程的步骤

The basic procedure follows a clear sequence. First, the desired gene (e.g., the human insulin gene) is isolated from the donor DNA. A restriction enzyme cuts the DNA at specific sites around the gene, producing sticky ends. The same restriction enzyme is used to cut open a plasmid vector, creating complementary sticky ends.

基本程序遵循清晰的顺序。首先，从供体DNA中分离出所需基因（如人胰岛素基因）。限制酶在基因周围的特定位点切割DNA，产生黏性末端。用同一种限制酶切开质粒载体，产生互补的黏性末端。

Next, the gene is mixed with the cut plasmids. The sticky ends pair up by complementary base pairing. DNA ligase is added to form permanent phosphodiester bonds, creating recombinant plasmids. These recombinant plasmids are introduced into host bacterial cells by a process called transformation, often using heat shock or calcium chloride treatment.

接下来，将基因与切开的质粒混合。黏性末端通过互补碱基配对结合。加入DNA连接酶形成永久的磷酸二酯键，产生重组质粒。这些重组质粒通过称为转化的过程导入宿主细菌细胞，通常采用热激或氯化钙处理。

The host bacteria are then cultured on agar plates containing an antibiotic. Only bacteria that have taken up the plasmid – carrying the antibiotic resistance marker – will survive and multiply. Finally, the colonies that express the desired gene are identified and grown in large fermenters to produce the protein product, such as insulin.

然后将宿主细菌在含有抗生素的琼脂平板上培养。只有摄取了质粒（携带抗生素抗性标记）的细菌才会存活并繁殖。最后，鉴定出表达所需基因的菌落，并在大型发酵罐中培养，以生产蛋白质产物，如胰岛素。

4. Insulin Production by Genetically Modified Bacteria | 转基因细菌生产胰岛素

One of the most important IGCSE examples is the manufacture of human insulin. Before genetic engineering, diabetics relied on insulin extracted from animal pancreases, which sometimes caused allergic reactions. Now, the human insulin gene is inserted into E. coli bacteria, which then produce human insulin identical to the body’s own.

IGCSE 最重要的例子之一是人胰岛素的制造。在基因工程之前，糖尿病患者依赖从动物胰腺提取的胰岛素，有时会引起过敏反应。现在，人胰岛素基因插入到大肠杆菌中，然后这些细菌产生与人体自身完全相同的人胰岛素。

The process involves isolating mRNA from human pancreatic cells, using reverse transcriptase to make complementary DNA (cDNA) without introns, and inserting it into a plasmid. The transgenic bacteria synthesise pure insulin, which is harvested, purified, and used by millions of patients worldwide.

这个过程包括从人胰腺细胞中分离mRNA，利用逆转录酶制造不含内含子的互补DNA（cDNA），并将其插入质粒。转基因细菌合成纯胰岛素，经过收集和纯化后，供全球数百万患者使用。

5. Genetically Modified Crops | 转基因作物

Plants can also be genetically modified to improve food production. Common traits introduced include herbicide resistance, insect resistance (such as Bt toxin gene from Bacillus thuringiensis), and improved nutritional content. For example, Golden Rice has been engineered to produce beta-carotene, tackling vitamin A deficiency in developing countries.

植物也可以通过基因工程来改善粮食生产。常见的导入性状包括抗除草剂性、抗虫性（如来自苏云金芽孢杆菌的Bt毒蛋白基因），以及提高营养成分。例如，黄金大米经过改造能产生β-胡萝卜素，以解决发展中国家的维生素A缺乏症。

Insect-resistant crops reduce the need for chemical pesticides, potentially lowering costs and environmental damage. However, there are concerns about the spread of transgenes to wild relatives via pollen, the evolution of resistant pests, and the long-term impact on ecosystems.

抗虫作物减少了对化学农药的需求，可能降低成本和环境破坏。但也有人担心转基因通过花粉传播到野生近缘种、害虫产生抗性，以及对生态系统的长期影响。

6. Gene Therapy | 基因治疗

Gene therapy involves inserting a functional allele of a gene into the cells of a patient suffering from a genetic disorder, such as cystic fibrosis or severe combined immunodeficiency (SCID). The normal allele is delivered using a viral vector, often a harmless adenovirus or retrovirus, which infects the target cells and introduces the therapeutic gene.

基因治疗是将一个功能正常的等位基因插入患有遗传病（如囊性纤维化或重症联合免疫缺陷 SCID）的病人细胞中。正常基因通过病毒载体递送，通常使用无害的腺病毒或逆转录病毒，感染靶细胞并导入治疗性基因。

However, gene therapy faces challenges: the inserted gene may not be expressed for long, the immune system might attack the viral vector, and the integration site in the genome can disrupt other essential genes, posing a risk of cancer.

然而，基因治疗面临挑战：插入的基因可能无法长期表达，免疫系统可能攻击病毒载体，在基因组中的整合位点可能破坏其他重要基因，存在致癌风险。

7. Polymerase Chain Reaction (PCR) – Amplifying DNA | 聚合酶链式反应 (PCR) – DNA扩增

Before genetic manipulation, scientists often need many copies of a specific DNA sequence. The polymerase chain reaction (PCR) is a technique used to amplify minute quantities of DNA rapidly. The process involves repeated cycles of three temperature steps: denaturation (about 95 °C) to separate DNA strands, annealing (50-65 °C) for primers to bind, and extension (72 °C) for Taq polymerase to synthesise new strands.

在进行基因操作之前，科学家通常需要大量特定DNA序列的拷贝。聚合酶链式反应（PCR）是一种快速扩增微量DNA的技术。过程包含三个温度步骤的重复循环：变性（约95°C）解开DNA双链，退火（50-65°C）使引物结合，延伸（72°C）由Taq聚合酶合成新链。

PCR is not strictly genetic engineering but is a vital supporting tool for obtaining enough DNA to work with. Taq polymerase, isolated from the thermophilic bacterium Thermus aquaticus, remains stable at high temperatures, making the cyclic process efficient.

PCR 严格来说并非基因工程，但却是获取足够工作量DNA的重要辅助工具。从嗜热菌水生栖热菌中分离出的Taq聚合酶，在高温下保持稳定，使循环过程高效。

8. Gel Electrophoresis – Separating DNA Fragments | 凝胶电泳 – 分离DNA片段

Gel electrophoresis is a technique used to separate DNA fragments based on size. After cutting DNA with restriction enzymes, the mixture of fragments is loaded into wells of an agarose gel. An electric current is applied; because DNA is negatively charged, fragments move towards the positive electrode. Smaller fragments travel faster and farther, creating a banding pattern that can be visualised using fluorescent dye or autoradiography.

凝胶电泳是一种根据大小分离DNA片段的技术。用限制酶切割DNA后，混合物载入琼脂糖凝胶的孔中。加上电流后，由于DNA带负电，片段向正极移动。较小的片段移动得更快更远，形成可以用荧光染料或放射自显影可见的条带图谱。

This technique is used in DNA profiling (paternity testing, forensics) and to check the success of genetic engineering procedures by confirming the presence of the desired gene fragment.

该技术用于DNA图谱分析（亲子鉴定、法医学），也用于通过确认所需基因片段的存在来检验基因工程操作是否成功。

9. Advantages and Applications Summary | 优点与应用总结

Application 应用	Benefit 益处
Insulin production 胰岛素生产	Human insulin is safer and cheaper; unlimited supply
GM crops (Bt corn, Golden Rice) 转基因作物	Higher yield, pest resistance, added nutrients, reduced pesticide use
Gene therapy 基因治疗	Potential to cure inherited diseases
Industrial enzymes 工业酶	Microorganisms produce enzymes for detergents, food processing

10. Disadvantages and Ethical Concerns | 缺点与伦理问题

Despite the benefits, genetic engineering raises several concerns. The insertion of a gene could have unintended side effects on the organism’s metabolism. In GM crops, the spread of antibiotic resistance marker genes to other bacteria is a health concern. There are fears that herbicide-resistant crops may lead to increased use of specific herbicides, harming biodiversity.

尽管有诸多好处，基因工程也引发了一些担忧。基因的插入可能对生物体的代谢产生意想不到的副作用。在转基因作物中，抗生素抗性标记基因传播到其他细菌是一个健康问题。有人担心抗除草剂作物可能导致特定除草剂的使用增加，损害生物多样性。

Ethically, people question whether it is right to alter the fundamental makeup of living things, especially animals and humans. The long-term ecological effects are unpredictable, and access to GM technology may widen the gap between rich and poor nations.

伦理方面，人们质疑改变生物（尤其是动物和人类）基本构造是否正确。长期的生态影响难以预测，而且转基因技术的获取可能加大富国与穷国之间的差距。

11. Key Terms Recap | 重要术语回顾

Recombinant DNA 重组DNA: DNA formed by joining pieces from different sources.
Sticky ends 黏性末端: Short, single-stranded overhangs created by restriction enzymes; allow base pairing with complementary sequences.
Vector 载体: A vehicle, often a plasmid, used to transfer genetic material into a host cell.
Transgenic organism 转基因生物: An organism that contains genetic material from another species.
Reverse transcriptase 逆转录酶: Enzyme that synthesises DNA from an RNA template, used to make cDNA from eukaryotic mRNA.

Published by TutorHao | IGCSE Biology Revision Series | aleveler.com

更多咨询请联系16621398022（同微信）

Genetic Engineering for IGCSE Biology | IGCSE 生物：基因工程 考点精讲