📚 Manipulating Genomes | 基因组操作技术
Manipulating genomes lies at the heart of modern biotechnology, from diagnosing inherited disease to engineering crops and developing gene therapies. This topic covers the core laboratory techniques that allow scientists to amplify, separate, sequence, and modify DNA.
基因组操作是现代生物技术的核心，从诊断遗传病到工程化作物和开发基因疗法都离不开它。本主题涵盖使科学家能够扩增、分离、测序和修饰 DNA 的核心实验技术。
1. DNA Amplification by PCR | PCR 扩增 DNA
Polymerase chain reaction (PCR) is a technique that amplifies a chosen DNA sequence millions of times in a few hours. It requires template DNA, a pair of primers, free deoxynucleotides, and Taq DNA polymerase.
聚合酶链式反应（PCR）是一种在几小时内将选定 DNA 序列扩增数百万倍的技术。它需要模板 DNA、一对引物、游离脱氧核苷酸和 Taq DNA 聚合酶。
The reaction runs through repeated thermal cycles. Denaturation at about 95 °C separates the double helix, annealing at 50-65 °C allows primers to bind to complementary sequences, and extension at 72 °C lets Taq polymerase synthesise new strands in the 5' to 3' direction.
反应经过反复的热循环。约 95 °C 变性使双螺旋分离，50-65 °C 退火使引物与互补序列结合，72 °C 延伸让 Taq 聚合酶沿 5' 到 3' 方向合成新链。
Because the products of each cycle become templates in the next cycle, the number of target copies increases exponentially.
由于每个循环的产物在下一个循环中成为模板，目标拷贝的数量呈指数增长。
2. Gel Electrophoresis | 凝胶电泳
Gel electrophoresis separates DNA fragments according to their length. DNA molecules carry a negative charge on their phosphate backbone, so they move towards the positive electrode when a voltage is applied.
凝胶电泳根据 DNA 片段的长度将其分离。DNA 分子的磷酸骨架带负电荷，因此施加电压时它们向正极移动。
Agarose gel acts as a molecular sieve: short fragments travel further than long fragments in the same time. A DNA ladder containing fragments of known sizes is run alongside the samples for comparison.
琼脂糖凝胶充当分子筛：相同时间内短片段比长片段迁移得更远。含有已知大小片段的 DNA 标记与样品并排电泳以便比较。
The separated bands are usually stained with a fluorescent dye such as ethidium bromide or SYBR Safe and visualised under UV light.
分离的条带通常用荧光染料（如溴化乙锭或 SYBR Safe）染色，并在紫外光下观察。
3. DNA Sequencing | DNA 测序
DNA sequencing reveals the precise order of bases along a DNA strand. In the Sanger method, DNA polymerase extends a primer in the presence of normal nucleotides and a small proportion of fluorescently labelled dideoxynucleotides.
DNA 测序揭示 DNA 链上碱基的精确顺序。在 Sanger 法中，DNA 聚合酶在正常核苷酸和少量荧光标记的双脱氧核苷酸存在下延伸引物。
When a dideoxynucleotide is incorporated, elongation stops because it lacks a 3' hydroxyl group. The resulting fragments end at each base position and are separated by capillary electrophoresis to read the sequence.
当双脱氧核苷酸被掺入时，由于缺少 3' 羟基，延伸终止。产生的片段在每个碱基位置终止，并通过毛细管电泳分离以读取序列。
Modern next-generation sequencing platforms carry out millions of sequencing reactions in parallel, making whole-genome sequencing much faster and cheaper.
现代新一代测序平台并行进行数百万个测序反应，使全基因组测序更快、更便宜。
4. DNA Profiling | DNA 谱分析
DNA profiling focuses on short tandem repeats (STRs), regions where short sequences such as AGAT are repeated a variable number of times. PCR primers flanking an STR locus amplify the region.
DNA 谱
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