Gene Mutations (IGCSE AQA Biology) | IGCSE AQA 生物：基因突变考点精讲

📚 Gene Mutations (IGCSE AQA Biology) | IGCSE AQA 生物：基因突变考点精讲

Gene mutations are permanent alterations in the DNA base sequence of a gene. They occur randomly and can have a range of effects on an organism, from no observable change to serious genetic disorders. For IGCSE AQA Biology, it is essential to understand how mutations arise, how they alter protein synthesis, and why they are crucial for variation and evolution. This guide covers all key points, using clear examples and exam-focused explanations.

基因突变是基因DNA碱基序列的永久性改变。它们随机发生，对生物体可能产生从无可见变化到严重遗传疾病的各种影响。对于IGCSE AQA生物，理解突变如何产生、如何改变蛋白质合成以及它们为何对变异和进化至关重要是必不可少的。本指南使用清晰的例子和面向考试的解释，涵盖所有关键点。

1. What is a Gene Mutation? | 什么是基因突变？

A gene mutation is a change in the sequence of nucleotide bases in the DNA of a gene. Genes are segments of DNA that code for a specific polypeptide. Therefore, any alteration in the base sequence may change the sequence of amino acids in the protein.

基因突变是基因DNA中核苷酸碱基序列的改变。基因是编码特定多肽的DNA片段。因此，碱基序列的任何改变都可能改变蛋白质中的氨基酸序列。

Mutations can occur in somatic cells, but these are not passed on to offspring. Only mutations that arise in gametes (sperm or egg cells) can be inherited and contribute to genetic variation in the next generation.

突变可以发生在体细胞中，但这些不会传递给后代。只有发生在配子（精子或卵细胞）中的突变才能遗传，并为下一代提供遗传变异。

A single gene mutation can be as small as one base pair change. Such a point mutation can have dramatic effects if it alters the active site of an enzyme or the shape of a structural protein.

单个基因突变可以小到只有一个碱基对的改变。如果这种点突变改变了酶的活性位点或结构蛋白的形状，就可能产生巨大的影响。

2. Causes of Mutations: Spontaneous and Induced | 突变的原因：自发与诱发

Spontaneous mutations occur naturally during DNA replication. DNA polymerase may insert an incorrect base, leading to a mispair. Although the cell has proofreading and repair mechanisms, some errors escape and become permanent.

自发突变在DNA复制过程中自然发生。DNA聚合酶可能插入一个错误的碱基，导致错配。尽管细胞具有校对和修复机制，但有些错误会逃脱并成为永久性的。

Induced mutations are caused by mutagens – physical or chemical agents that damage DNA. Ionising radiation (X-rays, gamma rays) can break the sugar-phosphate backbone. Ultraviolet (UV) light causes adjacent thymine bases to bond together, forming thymine dimers that distort the DNA helix.

诱发突变由诱变剂引起——即损伤DNA的物理或化学因素。电离辐射（X射线、伽马射线）可破坏糖-磷酸骨架。紫外线（UV）使相邻的胸腺嘧啶碱基键合在一起，形成胸腺嘧啶二聚体，扭曲DNA双螺旋。

Chemical mutagens include substances such as benzene, asbestos fibres, and nitrosamines. These chemicals can directly modify bases or insert themselves between bases (intercalation), leading to errors during replication. Even some viruses act as biological mutagens by integrating their DNA into the host genome.

化学诱变剂包括苯、石棉纤维和亚硝胺等物质。这些化学物质可以直接修饰碱基，或插入碱基之间（嵌入），导致复制错误。甚至某些病毒通过将其DNA整合到宿主基因组中而作为生物诱变剂发挥作用。

3. Mutagens and Mutation Rate | 诱变剂与突变率

The mutation rate is the frequency of new mutations in a single gene or organism over a given time. For most genes, the spontaneous mutation rate is very low, typically around 1 in 100,000 to 1 in 1,000,000 per replication.

突变率是单个基因或生物体在特定时间内新突变发生的频率。对于大多数基因，自发突变率非常低，通常每次复制约为十万分之一到百万分之一。

Exposure to mutagens greatly increases the

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