📚 7.15 The Genome and Genes | 7.15 基因组与基因
In Edexcel IGCSE Science (Double Award), specification point 7.15 covers a cornerstone of modern genetics: the relationship between DNA, genes, and the genome. This foundation is essential for understanding how organisms inherit traits and how proteins are produced. In this article, we break down these concepts clearly, with bilingual explanations to support your learning.
在Edexcel IGCSE科学（双奖）大纲中，考点7.15涵盖了现代遗传学的基石：DNA、基因和基因组之间的关系。这一基础对于理解生物如何遗传性状以及蛋白质如何产生至关重要。本文通过双语解说清晰分解这些概念，助力你的学习。
1. What is DNA? | 什么是 DNA？
Deoxyribonucleic acid (DNA) is a long molecule that carries the genetic instructions used in the growth, development, functioning and reproduction of all known organisms and many viruses.
脱氧核糖核酸（DNA）是一种长分子，携带着所有已知生物及许多病毒在生长、发育、功能和繁殖中所用的遗传指令。
DNA is a polymer made of repeating units called nucleotides. Each nucleotide consists of a phosphate group, a sugar called deoxyribose, and one of four nitrogenous bases: adenine (A), thymine (T), cytosine (C), or guanine (G).
DNA是一种聚合物，由称为核苷酸的重复单元构成。每个核苷酸包含一个磷酸基团、一种叫做脱氧核糖的糖，以及四种含氮碱基之一：腺嘌呤（A）、胸腺嘧啶（T）、胞嘧啶（C）或鸟嘌呤（G）。
The sequence of these bases along the DNA strand encodes genetic information, much like letters form words and sentences.
这些碱基沿DNA链的排列顺序编码遗传信息，就像字母组成词语和句子一样。
2. The Double-Helix Structure of DNA | DNA的双螺旋结构
DNA consists of two strands that wrap around each other to form a double helix. The two strands run in opposite directions (antiparallel), with 5′ ends and 3′ ends pointing in opposite ways.
DNA由两条链相互缠绕形成双螺旋。两条链方向相反（反向平行），5′端和3′端指向相反方向。
The bases on one strand pair with bases on the opposite strand through hydrogen bonds: adenine always pairs with thymine (A-T) and cytosine always pairs with guanine (C-G). This complementary base pairing ensures accurate copying of genetic information.
一条链上的碱基通过氢键与对侧链上的碱基配对：腺嘌呤总是与胸腺嘧啶配对（A-T），胞嘧啶总是与鸟嘌呤配对（C-G）。这种互补碱基配对确保了遗传信息的准确复制。
The double-helix model was proposed by James Watson and Francis Crick in 1953, based on X-ray diffraction data from Rosalind Franklin and Maurice Wilkins.
双螺旋模型由詹姆斯·沃森和弗朗西斯·克里克于1953年提出，依据是罗莎琳德·富兰克林和莫里斯·威尔金斯获得的X射线衍射数据。
3. Genes: Units of Hereditary Information | 基因：遗传信息的单位
A gene is a section of DNA that codes for a specific protein. The sequence of bases in a gene determines the order of amino acids in that protein.
基因是编码特定蛋白质的一段DNA。基因中的碱基序列决定了该蛋白质中氨基酸的顺序。
Genes can vary in length from a few hundred base pairs to over two million base pairs. Humans have approximately 20,000 to 25,000 protein-coding genes, which make up only about 1-2% of our total DNA.
基因的长度从几百个碱基对到超过两百万个碱基对不等。人类大约有20,000至25,000个蛋白质编码基因，仅占总DNA的1-2%。
Genes are located on chromosomes, and each gene occupies a specific position, or locus, on a chromosome.
基因位于染色体上，每个基因在染色体上占有特定的位置，即位点。
4. How a Gene Codes for a Protein | 基因如何编码蛋白质
A gene contains the instructions for assembling amino acids into a polypeptide chain that folds into a functional protein. The process occurs in two main stages: transcription and translation.
基因含有将氨基酸组装成多肽链并折叠成功能性蛋白质的指令。这个过程分为两个主要阶段：转录和翻译。
During transcription, the DNA double helix unwinds and one strand serves as a template to make a messenger RNA (mRNA) molecule. In RNA, the base uracil (U) replaces thymine, so adenine in DNA pairs with uracil in mRNA.
在转录过程中，DNA双螺旋解开，其中一条链作为模板合成信使RNA（mRNA）分子。在RNA中，碱基尿嘧啶（U）替代了胸腺嘧啶，因此DNA中的腺嘌呤与mRNA中的尿嘧啶配对。
The mRNA then leaves the nucleus and attaches to a ribosome. During translation, transfer RNA (tRNA) molecules bring amino acids to the ribosome according to the three-base codons on the mRNA. This builds the polypeptide chain step by step.
然后mRNA离开细胞核，附着在核糖体上。在翻译过程中，转运RNA（tRNA）分子根据mRNA上的三个碱基组成的密码子将氨基酸带到核糖体上，逐步构建多肽链。
DNA → RNA → Protein
This central dogma of molecular biology describes the flow of genetic information from DNA to RNA to protein.
这个分子生物学的中心法则描述了遗传信息从DNA流向RNA再到蛋白质的过程。
5. The Genome: The Complete Set of DNA | 基因组：全套 DNA
The genome is the entire DNA of an organism, including all of its genes and the non-coding sequences between them. It contains the full set of hereditary information needed to build and maintain that organism.
基因组是生物体的全套DNA，包括其所有基因以及基因之间的非编码序列。它包含了构建和维持该生物所需的全部遗传信息。
In humans, the genome consists of about 3 billion base pairs of DNA distributed across 23 pairs of chromosomes in the nucleus, plus a small amount of DNA in the mitochondria.
在人类中，基因组包含约30亿个碱基对的DNA，分布在细胞核中的23对染色体上，以及线粒体中的少量DNA。
Not all of the genome codes for proteins. Many non-coding regions play regulatory roles, such as controlling when and where genes are switched on or off.
并非所有基因组都编码蛋白质。许多非编码区域起调控作用，例如控制基因在何时何地开启或关闭。
6. Why the Human Genome Project Matters | 人类基因组计划为何重要
The Human Genome Project (HGP) was an international research effort completed in 2003 that determined the sequence of all 3 billion base pairs in human DNA. This achievement has transformed medicine and biology.
人类基因组计划（HGP）是一项于2003年完成的国际科研项目，测定了人类DNA全部30亿个碱基对的序列。这一成就改变了医学和生物学。
Knowing the genome sequence allows scientists to identify genes associated with inherited diseases, such as cystic fibrosis or sickle cell anaemia, paving the way for early diagnosis and gene therapy.
了解基因组序列可使科学家识别与遗传病（如囊性纤维化或镰刀型细胞贫血）相关的基因，为早期诊断和基因治疗铺平道路。
The HGP also aids in understanding human evolution, tracking ancient human migrations, and developing personalised medicine, where treatments are tailored to an individual's genetic makeup.
HGP还有助于理解人类进化、追踪古人类迁徙，以及开发个性化医疗，即根据个体的基因组成量身定制治疗方案。
Furthermore, it has advanced forensic science by improving DNA profiling techniques used in criminal investigations and paternity tests.
此外，通过改进用于刑事调查和亲子鉴定的DNA指纹技术，它也推动了法医学的发展。
7. Chromosomes: Packages of DNA | 染色体：DNA的包装
In eukaryotic cells, DNA is tightly wrapped around proteins called histones to form structures known as chromosomes. This packaging allows metres of DNA to fit inside the tiny nucleus of a cell.
在真核细胞中，DNA紧密缠绕在称为组蛋白的蛋白质周围，形成称为染色体的结构。这种包装使数米长的DNA能够装进细胞微小的细胞核内。
Humans have 46 chromosomes (23 pairs) in most body cells. One chromosome of each pair is inherited from the mother and the other from the father. Sex is determined by the 23rd pair: XX for females and XY for males.
人类大多数体细胞有46条染色体（23对），每对染色体中的一条来自母亲，另一条来自父亲。性别由第23对染色体决定：XX为女性，XY为男性。
Each chromosome carries hundreds to thousands of genes. The karyotype, a picture of an individual's full set of chromosomes, can reveal chromosomal abnormalities such as Down syndrome (trisomy 21).
每条染色体携带数百到数千个基因。核型图显示个体全套染色体，可以揭示染色体异常，如唐氏综合征（21三体）。
8. From Genotype to Phenotype | 从基因型到表型
An organism's genotype is the combination of alleles (different forms of a gene) it possesses for a particular trait. The phenotype is the observable characteristic that results from the interaction of the genotype with the environment.
生物的基因型是指其针对某一性状所拥有的等位基因（基因的不同形式）组合。表型是基因型与环境相互作用产生的可观察特征。
For example, a person may inherit alleles for tallness, but poor nutrition during childhood can limit height. Thus, the final height (phenotype) is not determined by genes alone.
例如，一个人可能遗传了高个子的等位基因，但儿时营养不良会限制身高。因此，最终身高（表型）并非仅由基因决定。
Some traits, such as blood type in humans, are largely determined by genotype with little environmental influence. Understanding the genotype-phenotype link helps breeders select desirable traits in agriculture and informs medical risk assessments.
有些性状，如人类的血型，主要由基因型决定，受环境影响很小。理解基因型与表型的联系有助于育种者选择优良农业性状，并为医学风险评估提供信息。
9. Mutations: Changes in the DNA Sequence | 突变：DNA序列的改变
A mutation is a permanent change in the nucleotide sequence of DNA. Mutations can occur spontaneously during DNA replication or be induced by mutagens such as UV radiation, certain chemicals, or viruses.
突变是DNA核苷酸序列的永久性改变。突变可在DNA复制时自发发生，或由诱变剂（如紫外线、某些化学物质或病毒）诱导产生。
Mutations may be harmful, neutral, or very rarely beneficial. For example, a single base substitution in the gene for haemoglobin causes sickle cell anaemia, a serious blood disorder that decreases oxygen delivery.
突变可能有害、中性或（极少数情况下）有益。例如，血红蛋白基因中单个碱基的替换导致镰刀型细胞贫血——一种降低氧气输送的严重血液疾病。
On the other hand, some mutations provide a survival advantage. A mutation in the CCR5 gene offers resistance to HIV infection, illustrating how genetic variation can drive evolution.
另一方面，某些突变提供生存优势。CCR5基因的一个突变使人对HIV感染具有抵抗力，这体现了遗传变异如何驱动进化。
When a mutation occurs in a gene, it can alter the amino acid sequence of the protein, potentially changing its shape and function. In some cases, a stop codon appears prematurely, producing a truncated, non-functional protein.
当基因发生突变时，可能改变蛋白质的氨基酸序列，进而改变其形状和功能。某些情况下，提前出现的终止密码子会产生截短且无功能的蛋白质。
10. Applications: Medicine, Forensics and Beyond | 应用：医学、法医学及其他
Understanding genes and the genome has led to powerful real-world applications. Genetic testing can identify whether an individual carries alleles for disorders such as Huntington disease, allowing informed family planning.
对基因和基因组的理解带来了强大的实际应用。基因检测可以识别个体是否携带亨廷顿病等疾病的等位基因，以便做出知情的家庭规划。
Gene therapy aims to treat genetic disorders by inserting a functional gene into a patient's cells to compensate for a faulty one. Although still experimental for many conditions, it has shown success in treating severe combined immunodeficiency (SCID).
基因疗法旨在通过将功能基因插入患者细胞中来补偿缺陷基因，从而治疗遗传病。尽管对许多疾病仍处实验阶段，但已在治疗重症联合免疫缺陷（SCID）方面取得成功。
In forensic science, DNA profiling uses short tandem repeats (STRs) from non-coding regions to generate a DNA fingerprint that is unique to each individual (except identical twins). This technique is widely used to identify suspects in criminal cases or establish paternity.
在法医学中，DNA分析使用非编码区的短串联重复序列（STR）生成每个人独一无二的DNA指纹（同卵双胞胎除外）。该技术广泛用于识别刑事案件中的嫌疑人或确认亲子关系。
Beyond healthcare, genetic engineering in agriculture has produced crops resistant to pests, herbicides, or harsh environmental conditions, improving food security worldwide.
在医疗保健之外，农业中的基因工程已培育出抗虫、抗除草剂或耐恶劣环境条件的作物，提高了全球粮食安全。
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