📚 Genetic Technology and Agriculture | 基因技术与农业
Genetic technology has transformed agriculture by allowing specific genes to be transferred, altered or edited within crop genomes. For Cambridge A-Level Biology, you need to understand the tools of gene manipulation, how GM crops are engineered, and how their benefits and risks are evaluated.
基因技术通过允许在作物基因组中转移、改变或编辑特定基因，已经改变了农业。对剑桥 A-Level 生物来说，你需要理解基因操作的工具、转基因作物是如何构建的，以及如何评估其收益与风险。
1. What Is Genetic Technology? | 什么是基因技术？
Genetic technology, also called genetic engineering or recombinant DNA technology, involves the direct manipulation of an organism’s DNA. In agriculture it is used to add, remove or alter genes that control traits such as yield, nutritional content and pest resistance.
基因技术，也称基因工程或重组 DNA 技术，涉及对生物体 DNA 的直接操作。在农业中，它被用来添加、去除或改变控制产量、营养含量和抗虫性等性状的基因。
A transgenic organism contains DNA from a different species, whereas a cisgenic organism receives genes from the same or a closely related species. Genome editing, especially CRISPR-Cas9, can alter existing sequences without necessarily introducing foreign DNA.
转基因生物含有来自不同物种的 DNA，而顺基因生物接受来自同一物种或近缘物种的基因。基因组编辑，尤其是 CRISPR-Cas9，可以在不一定引入外源 DNA 的情况下改变现有序列。
2. Core Tools: Restriction Enzymes and Ligase | 核心工具：限制酶与连接酶
Restriction endonucleases cut DNA at specific recognition sequences, often producing sticky ends with short single-stranded overhangs. These complementary sticky ends allow DNA fragments from different sources to anneal.
限制性内切酶在特定识别序列处切割 DNA，通常产生带有短单链突出的黏性末端。这些互补的黏性末端使来自不同来源的 DNA 片段能够退火结合。
DNA ligase then seals the sugar-phosphate backbone by forming phosphodiester bonds. In a typical cloning experiment, the gene of interest and the vector are cut with the same restriction enzyme to create compatible ends.
随后 DNA 连接酶通过形成磷酸二酯键封闭糖-磷酸骨架。在典型的克隆实验中，目的基因和载体用同一种限制酶切割，以产生相容末端。
Reverse transcriptase can also be used to make complementary DNA (cDNA) from mRNA. This is useful because cDNA lacks introns and can be expressed more easily in bacterial or plant systems.
逆转录酶也可用于从 mRNA 制备互补 DNA (cDNA)。这很有用，因为 cDNA 没有内含子，可以在细菌或植物系统中更容易地表达。
3. Vectors and Gene Transfer in Plants | 植物中的载体与基因转移
A vector is a carrier DNA molecule used to deliver the gene of interest into a host cell. In plants, the most widely used vector is the Ti plasmid from Agrobacterium tumefaciens.
载体是用于将目的基因送入宿主细胞的运载 DNA 分子。在植物中，使用最广泛的载体是来自根癌农杆菌的 Ti 质粒。
The Ti plasmid naturally transfers a segment of DNA called T-DNA into plant cells, causing crown gall disease. Scientists remove the disease-causing genes but keep the T-DNA border sequences, then insert the desired gene between them.
Ti 质粒天然将一段称为 T-DNA 的 DNA 转入植物细胞，引起冠瘿病。科学家去除致病基因但保留 T-DNA 边界序列，然后将所需基因插入两者之间。
Alternative methods include microprojectile bombardment, where DNA-coated gold or tungsten particles are fired into plant cells, and electroporation, which uses brief electric pulses to make cell membranes permeable to DNA.
替代方法包括微弹轰击法，即将包裹 DNA 的金粉或钨粉颗粒高速射入植物细胞；以及电穿孔法，利用短暂电脉冲使细胞膜对 DNA 通透。
4. Promoters, Markers and Transgene Expression | 启动子、标记基因与转基因表达
For a transgene to be expressed, it must be linked to a promoter and a terminator. The cauliflower mosaic virus 35S promoter (CaMV 35S) is commonly used because it drives high-level constitutive expression in most plant tissues.
要使转基因表达，它必须与启动子和终止子相连。花椰菜花叶病毒 35S 启动子（CaMV 35S）常用，因为它能在大多数植物组织中驱动高水平的组成型表达。
A selectable marker gene, such as neomycin phosphotransferase II (nptII) conferring kanamycin resistance, allows transformed cells to be identified. Only cells that have taken up the vector survive on a medium containing the selective agent.
选择标记基因，例如赋予卡那霉素抗性的新霉素磷酸转移酶 II（nptII），可用于鉴定转化细胞。只有吸收了载体的细胞才能在含选择剂的培养基上存活。
Reporter genes such as green fluorescent protein (GFP) or β-glucuronidase (GUS) can confirm gene expression visually or by colorimetric assay. However, antibiotic resistance marker genes may raise concerns about potential transfer to bacteria.
报告基因如绿色荧光蛋白（GFP）或 β-葡萄糖醛酸酶（GUS）可通过视觉或比色法确认基因表达。然而，抗生素抗性标记基因可能引发对抗性基因向细菌转移的担忧。
5. Herbicide-Tolerant Crops | 抗除草剂作物
Herbicide-tolerant GM crops allow farmers to spray broad-spectrum herbicides such as glyphosate without killing the crop. Glyphosate inhibits the enzyme EPSPS, which is needed for synthesis of aromatic amino acids.
抗除草剂转基因作物允许农民喷洒草甘膦等广谱除草剂而不会杀死作物。草甘膦抑制 EPSPS 酶，该酶是合成芳香族氨基酸所必需的。
One strategy inserts a bacterial EPSPS variant that is not inhibited by glyphosate, so the shikimate pathway continues. Another strategy uses a gene that encodes an enzyme degrading the herbicide, such as phosphinothricin acetyltransferase (pat/bar) for glufosinate.
一种策略是插入不受草甘膦抑制的细菌 EPSPS 变体，使莽草酸途径继续运行。另一种策略使用编码降解除草剂的酶的基因，例如针对草铵膦的草丁膦乙酰转移酶（pat/bar）。
This technology can reduce soil erosion by encouraging no-till farming. However, it may also increase herbicide use and select for herbicide-resistant weeds if not managed carefully.
该技术可通过鼓励免耕农业减少土壤侵蚀。但如果管理不当，也可能增加除草剂用量并筛选出抗除草剂杂草。
6. Insect-Resistant Bt Crops | 抗虫 Bt 作物
Bt crops contain cry genes from the soil bacterium Bacillus thuringiensis. These genes produce Cry proteins that are toxic to specific insect groups, such as lepidopteran larvae, after ingestion in alkaline insect guts.
Bt 作物含有来自土壤细菌苏云金芽孢杆菌的 cry 基因。这些基因产生 Cry 蛋白，在昆虫碱性的肠道中被摄入后，对特定昆虫类群（如鳞翅目幼虫）有毒。
The Cry toxin binds to receptors on the midgut epithelial cells, causing pore formation and cell lysis. Humans and most non-target organisms lack these receptors and have acidic stomachs, so the protein is rapidly digested.
Cry 毒素与中肠上皮细胞上的受体结合，引起孔洞形成和细胞裂解。人类和大多数非靶标生物缺少这些受体，且胃部呈酸性，因此该蛋白质会被迅速消化。
Bt crops reduce the need for chemical insecticides and can protect yield. Continuous exposure creates selection pressure for resistant insect populations, so refuge strategies are used to delay resistance evolution.
Bt 作物减少了对化学杀虫剂的需求，并能保护产量。持续暴露会产生选择压力，使抗性昆虫群体出现，因此采用庇护所策略来延缓抗性进化。
7. Nutritional Enhancement: Golden Rice | 营养强化：黄金大米
Golden Rice is genetically engineered to produce β-carotene in the endosperm of rice grains. It contains two key genes: psy from daffodil or maize and crtI from a soil bacterium, which complete the β-carotene biosynthetic pathway.
黄金大米经过基因工程改造，在稻米胚乳中产生 β-胡萝卜素。它含有两个关键基因：来自黄水仙或玉米的 psy 和来自土壤细菌的 crtI，它们补全了 β-胡萝卜素生物合成途径。
β-carotene is a provitamin A that the human body can convert into retinol (vitamin A). Golden Rice was developed to reduce vitamin A deficiency, which causes preventable blindness and increased mortality in regions dependent on rice.
β-胡萝卜素是一种维生素 A 原，人体可将其转化为视黄醇（维生素 A）。黄金大米旨在减少维生素 A 缺乏症，该病在以稻米为主食的地区导致可预防的失明和死亡率升高。
Field trials show that a reasonable daily intake of Golden Rice can supply a significant proportion of vitamin A needs. Critics argue that dietary diversity and supplementation may be more culturally acceptable alternatives.
田间试验表明，合理的每日黄金大米摄入量可提供相当比例的维生素 A 需求。批评者认为，饮食多样化和补充剂可能是文化上更容易接受的替代方案。
8. Disease-Resistant and Stress-Tolerant Crops | 抗病与抗逆作物
Genetic technology can confer
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