📚 6.4 Cloning & Biotechnology | 6.4 克隆与生物技术
This unit links two core areas of modern biology: cloning, which produces genetically identical copies of organisms, cells or DNA, and biotechnology, which uses living organisms to make useful products. Understanding these processes is essential for A-level biology because they integrate cell biology, genetics, microbiology and practical techniques.
本单元连接现代生物学的两个核心领域：克隆与生物技术。克隆产生基因完全相同的生物体、细胞或 DNA 拷贝，而生物技术利用活的生物体制造有用产品。理解这些过程对 A-level 生物至关重要，因为它们整合了细胞生物学、遗传学、微生物学和实验技术。
1. Cloning: Definition and Natural Clones | 克隆：定义与天然克隆
Cloning is the production of genetically identical copies of an organism, cell, or DNA molecule. Natural clones occur widely in asexual reproduction, such as binary fission in bacteria, budding in yeast, and vegetative propagation in plants.
克隆是指产生基因完全相同的生物体、细胞或 DNA 分子拷贝。天然克隆广泛存在于无性生殖中，例如细菌的二分裂、酵母的出芽生殖以及植物的营养繁殖。
In animals, identical twins are natural clones because they arise from the same fertilised egg that splits into two embryos. However, the term 'clone' can also refer to gene cloning, where a specific gene is copied using recombinant DNA technology.
在动物中，同卵双胞胎是天然克隆，因为它们来自同一个受精卵分裂形成的两个胚胎。不过，'克隆'一词也可指基因克隆，即利用重组 DNA 技术复制特定基因。
Many plants naturally produce runners, bulbs, tubers or rhizomes. For example, strawberry runners and potato tubers allow a single parent plant to produce many genetically identical offspring without fertilisation.
许多植物天然产生匍匐茎、鳞茎、块茎或根茎。例如，草莓的匍匐茎和马铃薯的块茎使一株亲本植物无需受精即可产生许多基因相同的后代。
2. Artificial Plant Cloning: Cuttings and Micropropagation | 人工植物克隆：扦插与微繁殖
Many plants can be cloned artificially from cuttings. A stem or leaf cutting is taken from a parent plant and placed in moist soil or water, where it develops roots and grows into a new plant. This exploits totipotency and produces offspring that are genetically identical to the parent.
许多植物可以通过扦插进行人工克隆。从亲本植株上取一段茎或叶插条，放入湿润土壤或水中，插条长出根并发育为新植株。这利用了植物细胞的全能性，产生的后代与亲本基因完全相同。
Micropropagation is a more advanced technique used on a commercial scale. Small pieces of meristem tissue called explants are surface-sterilised, placed on sterile nutrient agar containing plant hormones, and grown into callus tissue. The callus is then subdivided repeatedly to produce thousands of plantlets under controlled conditions.
微繁殖是一种更先进的商业规模技术。将小块分生组织（外植体）进行表面消毒，置于含植物激素的无菌营养琼脂上，培养成愈伤组织。随后反复分割愈伤组织，在受控条件下培育出数千株小苗。
A key advantage of micropropagation is that it can produce large numbers of disease-free plants quickly. However, it is labour-intensive and can be expensive, and the lack of genetic variation makes crops vulnerable to new diseases.
微繁殖的一个关键优点是能快速生产大量无病植株。但该方法劳动密集、成本较高，而且缺乏遗传变异会使作物更容易遭受新病害的侵袭。
3. Artificial Animal Cloning: Somatic Cell Nuclear Transfer | 人工动物克隆：体细胞核移植
Somatic cell nuclear transfer (SCNT) is the main method of cloning adult mammals. It involves removing the nucleus from an unfertilised egg cell, replacing it with the nucleus of a differentiated somatic cell from the animal to be cloned, and stimulating the reconstructed egg to divide by an electric shock.
体细胞核移植（SCNT）是克隆成年哺乳动物的主要方法。该方法先去除未受精卵细胞的细胞核，用待克隆动物分化的体细胞核替换，再通过电击刺激重组卵分裂。
The resulting embryo is implanted into a surrogate mother, and the offspring is genetically identical to the donor of the somatic cell nucleus. Dolly the sheep, born in 1996, was the first mammal cloned from an adult somatic cell.
所得胚胎被植入代孕母体，其后代与体细胞核供体基因完全相同。1996 年出生的绵羊多莉是第一只由成年体细胞克隆的哺乳动物。
SCNT has low efficiency, many embryos fail to develop, and clones may suffer from premature ageing or abnormalities due to incomplete reprogramming of the donor nucleus.
体细胞核移植效率较低，许多胚胎无法正常发育，并且由于供体核重编程不完全，克隆个体可能出现早衰或发育异常。
4. Biotechnology and Microorganisms: An Overview | 生物技术与微生物：概述
Biotechnology is the industrial use of living organisms or their components to make useful products. Microorganisms such as bacteria and fungi are especially useful because they grow rapidly, have simple nutrient requirements, and can be genetically engineered.
生物技术是指利用活的生物体或其组分进行工业规模生产有用产品的技术。细菌和真菌等微生物特别有用，因为它们生长迅速、营养需求简单，并且可以进行基因工程改造。
In food production, yeast Saccharomyces cerevisiae is used in bread and alcohol production, while fungi such as Penicillium produce antibiotics. Bacteria such as Lactobacillus are used in yoghurt production, and genetically modified E. coli can produce human insulin.
在食品生产中，酿酒酵母用于面包和酒精生产，青霉等真菌产生抗生素。乳酸菌用于酸奶生产，而经基因改造的大肠杆菌可以生产人胰岛素。
Microorganisms can be cultured in fermenters under controlled temperature, pH, oxygen and nutrient levels. Their products may be intracellular or extracellular, and downstream processing is needed to isolate and purify the product.
微生物可在发酵罐中培养，控制温度、pH、氧气和营养物水平。其产物可以是胞内的或胞外的，需要经过下游加工来分离和纯化产物。
5. Fermentation: Batch and Continuous Cultures | 发酵：分批培养与连续培养
Fermentation is the mass culture of microorganisms to produce a desired product. In batch fermentation, the fermenter is set up with fresh nutrients, inoculated with microorganisms, and allowed to run until the nutrients are used up or product yield peaks. The vessel is then emptied, cleaned and restarted.
发酵是指大规模培养微生物以获得所需产物的过程。在分批发酵中，发酵罐内加入新鲜营养物质并接种微生物，运行至营养耗尽或产物产量达到峰值。随后排空、清洗并重新开始。
In continuous fermentation, fresh nutrient medium is added continuously while culture medium and product are removed at the same rate. This maintains exponential growth and is more efficient for high-volume products such as insulin or bioethanol.
在连续发酵中，新鲜培养基连续加入，同时以相同速率移出培养液和产物。这样可以维持指数生长，对于胰岛素或生物乙醇等大批量产品效率更高。
A batch culture goes through lag, log, stationary and death phases, whereas a continuous culture can be kept in the log phase. However, continuous cultures are more susceptible to contamination and require reliable monitoring equipment.
分批培养经历延滞期、对数期、稳定期和死亡期，而连续培养可以保持在对数期。但连续培养更容易受到污染，并且需要可靠的监测设备。
6. Aseptic Technique and Contamination Control | 无菌操作与污染控制
Successful biotechnology depends on aseptic technique, which prevents unwanted microorganisms from entering cultures or products. Contamination can reduce yield, produce toxic by-products, and make downstream purification difficult.
成功的生物技术依赖无菌操作，防止不需要的微生物进入培养物或产品。污染会降低产量、产生有毒副产物，并使下游纯化变得困难。
Common aseptic methods include sterilising culture media and equipment by autoclaving at 121 °C for about 15 minutes, passing air through filters, using sterile inoculating loops, and working near a Bunsen flame to create an upward air current.
常见的无菌方法包括：将培养基和设备在 121 °C 高压灭菌约 15 分钟，使空气通过过滤器，使用无菌接种环，以及在酒精灯火焰附近操作以形成上升气流。
In micropropagation, explants are surface-sterilised with dilute bleach or ethanol, and all agar media and instruments are autoclaved. In animal cell culture, laminar flow hoods and antibiotics are used to maintain sterility.
在微繁殖中，外植体用稀漂白剂或乙醇进行表面消毒，所有琼脂培养基和器械均高压灭菌。在动物细胞培养中，使用层流净化台和抗生素来维持无菌环境。
7. Immobilised Enzymes and Downstream Processing | 固定化酶与下游加工
Enzymes are often used in biotechnology because they are specific and work under mild conditions. To make processes more efficient, enzymes can be immobilised by adsorption, covalent bonding, or entrapment in a gel matrix such as alginate beads.
酶在生物技术中常用，因为它们专一性强且反应条件温和。为提高效率，酶可通过吸附、共价结合或包埋在海藻酸盐珠等凝胶基质中实现固定化。
Immobilised enzymes can be reused, separated easily from products, and often show greater stability to temperature and pH changes. A typical application is immobilised lactase converting lactose into glucose and galactose in lactose-free milk.
固定化酶可以重复使用，容易与产物分离，并且通常对温度和 pH 变化具有更高的稳定性。一个典型应用是固定化乳糖酶将乳糖转化为葡萄糖和半乳糖，用于生产无乳糖牛奶。
Downstream processing refers to the separation and purification steps after fermentation or enzyme reaction. These may include centrifugation, filtration, chromatography and crystallisation, depending on whether the product is intracellular or extracellular.
下游加工是指发酵或酶反应后的分离和纯化步骤。根据产物是胞内还是胞外，可包括离心、过滤、色谱和结晶等步骤。
8. Growth Curves and Factors Affecting Microbial Growth | 生长曲线与影响微生物生长的因素
A closed batch culture shows a characteristic growth curve. In the lag phase, cells synthesise enzymes and adapt to the new environment; in the log or exponential phase, the population doubles at a constant rate; in the stationary phase, nutrient depletion and waste accumulation make birth rate equal to death rate; finally, in the death phase, cells die at an exponential rate.
封闭的分批培养表现出典型的生长曲线。延滞期细胞合成酶并适应新环境；对数期（指数期）种群以恒定速率倍增；稳定期由于营养耗尽和废物积累，出生率与死亡率相等；最后在死亡期，细胞以指数速率死亡。
The growth rate can be calculated using the population doubling time. If N₀ is the initial cell number and Nₜ is the number after time t, the number of generations n is given by:
生长速率可用群体倍增时间计算。如果 N₀ 为初始细胞数，Nₜ 为 t 时间后的细胞数，则世代数 n 可由下式得出：
n = (log Nₜ − log N₀) / log 2
Limiting factors include temperature, pH, oxygen availability, and nutrient concentration. Deviation from the optimum reduces enzyme activity and membrane function, lowering the growth rate.
限制因素包括温度、pH、氧气供应和营养物浓度。偏离最适条件会降低酶活性和膜功能，从而降低生长速率。
9. Applications of Cloning and Biotechnology in Medicine and Agriculture | 克隆与生物技术在医药和农业中的应用
Gene cloning and genetic modification allow the production of human therapeutic proteins. For example, the gene for human insulin is inserted into a plasmid vector and expressed in E. coli or yeast, providing a safe and reliable source of insulin for diabetic patients.
基因克隆和基因改造可以生产人类治疗性蛋白质。例如，将人胰岛素基因插入质粒载体并在大肠杆菌或酵母中表达，为糖尿病患者提供安全可靠的胰岛素来源。
In agriculture, cloned transgenic animals can produce pharmaceuticals in their milk, a process called pharming. For example, sheep have been engineered to produce human blood clotting factors or antibodies in milk.
在农业中，克隆的转基因动物可在乳汁中生产药物，这一过程称为动物制药。例如，已有绵羊经改造后在乳汁中产生人凝血因子或抗体。
Plant cloning is used to preserve rare cultivars and to produce uniform, disease-free planting material for crops such as bananas, potatoes and ornamental plants. It also helps in conserving endangered plant species through tissue culture.
植物克隆用于保存珍稀栽培品种，并为香蕉、马铃薯和观赏植物等作物生产整齐一致的无病种植材料。它还通过组织培养帮助保护濒危植物物种。
10. Ethical, Social and Safety Issues | 伦理、社会与安全问题
Cloning and biotechnology raise important ethical questions. Animal cloning can cause suffering and high rates of miscarriage
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