📚 DNA Molecules and Genetic Experiments | DNA分子与遗传实验解读
DNA is the blueprint of life. It contains the instructions needed for an organism to develop, survive and reproduce. Scientists have conducted many experiments to understand how genetic information is passed from one generation to the next. In this article, we will explore the structure of DNA, how it works, and some famous genetic experiments that revealed the secrets of heredity.
DNA是生命的蓝图。它包含了生物体发育、生存和繁殖所需的指令。科学家们进行了许多实验，以了解遗传信息是如何代代相传的。在本文中，我们将探索DNA的结构、它如何工作，以及一些揭示了遗传奥秘的著名遗传实验。
1. What is DNA? | 什么是DNA？
DNA stands for deoxyribonucleic acid. It is a long molecule found in almost every cell of your body. DNA stores genetic information that determines your traits, such as eye colour, hair type, and even some aspects of your personality.
DNA是脱氧核糖核酸的缩写。它是一种长分子，几乎存在于你身体的每一个细胞中。DNA储存着决定你性状的遗传信息，比如眼睛颜色、头发类型，甚至是你个性的某些方面。
Every living organism, from bacteria to humans, uses DNA to pass on hereditary information. The DNA in each of your cells is organised into structures called chromosomes.
从细菌到人类，每个生物体都利用DNA来传递遗传信息。你每个细胞中的DNA被组织成叫做染色体的结构。
DNA is often compared to a recipe book. Just as a recipe book contains step-by-step instructions for making a cake, DNA contains the instructions for building an organism. These instructions are written in a chemical code made up of four bases: adenine (A), thymine (T), cytosine (C) and guanine (G).
DNA常被比作一本食谱书。正如食谱书包含制作蛋糕的逐步说明，DNA包含构建生物体的指令。这些指令是用由四种碱基组成的化学密码写成的：腺嘌呤（A）、胸腺嘧啶（T）、胞嘧啶（C）和鸟嘌呤（G）。
2. The Structure of DNA | DNA的结构
In 1953, James Watson and Francis Crick discovered the double helix structure of DNA. This shape looks like a twisted ladder. The sides of the ladder are made of sugar and phosphate groups, while the rungs consist of pairs of nitrogenous bases.
1953年，詹姆斯·沃森和弗朗西斯·克里克发现了DNA的双螺旋结构。这种形状看起来像一个扭曲的梯子。梯子的两侧由糖和磷酸基团构成，而梯级则由成对的含氮碱基组成。
The base pairing rules are very specific: adenine always pairs with thymine (A–T), and cytosine always pairs with guanine (C–G). These pairs are held together by weak hydrogen bonds, which can be broken when the DNA needs to be copied.
碱基配对规则非常特殊：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）。这些配对由微弱的氢键维系，当DNA需要复制时，这些键可以断开。
Because of this complementary base pairing, each strand of DNA can serve as a template for building a new partner strand. This is essential for reproduction and cell division.
由于这种互补碱基配对，DNA的每条链都可以作为模板，用于构建一条新的搭档链。这对繁殖和细胞分裂至关重要。
3. DNA Replication | DNA复制
Before a cell divides, it must copy all of its DNA so that each new cell receives a complete set of genetic instructions. This process is called DNA replication. The double helix unwinds, and an enzyme called DNA helicase breaks the hydrogen bonds between the bases, separating the two strands.
在细胞分裂之前，它必须复制所有的DNA，以便每个新细胞获得一套完整的遗传指令。这个过程称为DNA复制。双螺旋解开，一种叫做DNA解旋酶的酶断开碱基之间的氢键，将两条链分开。
Then, another enzyme called DNA polymerase moves along each strand and adds new complementary nucleotides. As a result, two identical DNA molecules are formed, each containing one original strand and one newly synthesised strand. This is known as semi-conservative replication.
然后，另一种叫做DNA聚合酶的酶沿着每条链移动，添加新的互补核苷酸。结果形成两个相同的DNA分子，每个分子包含一条原始链和一条新合成的链。这被称为半保留复制。
The accuracy of DNA replication is remarkable, but sometimes mistakes happen. These mistakes are called mutations, and they can lead to changes in an organism’s traits.
DNA复制的准确性非常惊人，但有时也会出错。这些错误称为突变，它们会导致生物体性状的改变。
4. Genes and Chromosomes | 基因与染色体
A gene is a segment of DNA that codes for a specific protein or trait. Humans have about 20,000–25,000 genes. These genes are packaged into 46 chromosomes, which are found in the nucleus of most cells. You inherit 23 chromosomes from your mother and 23 from your father.
基因是编码特定蛋白质或性状的一段DNA。人类大约有20,000到25,000个基因。这些基因被包装成46条染色体，存在于大多数细胞的细胞核中。你从母亲那里继承23条染色体，从父亲那里继承23条。
Not all of your DNA codes for proteins. Some regions regulate gene activity, turning genes on or off in different cells. This is why a muscle cell and a nerve cell can look and function very differently, even though they contain the same DNA.
并非你的所有DNA都编码蛋白质。有些区域调控基因活性，在不同细胞中开启或关闭基因。这就是为什么肌肉细胞和神经细胞虽然含有相同的DNA，但外观和功能却大相径庭。
Genes come in different versions called alleles. For example, the gene for eye colour may have a brown allele and a blue allele. The combination of alleles you inherit determines your phenotype, or observable characteristics.
基因有不同的版本，称为等位基因。例如，眼睛颜色的基因可能有一个棕色等位基因和一个蓝色等位基因。你继承的等位基因组合决定了你的表型，即可观察到的特征。
5. Mendel’s Pea Plant Experiments | 孟德尔的豌豆实验
Gregor Mendel, an Austrian monk, is often called the father of genetics. In the mid-1800s, he performed experiments on pea plants to study how traits are inherited. He chose pea plants because they grow quickly and have several distinct characteristics, such as tall vs. short stems and yellow vs. green seeds.
奥地利修道士格雷戈尔·孟德尔常被称为遗传学之父。在19世纪中期，他用豌豆植物进行实验，研究性状是如何遗传的。他选择豌豆植物是因为它们生长迅速，并且有几种明显的特征，例如高茎与矮茎、黄种子与绿种子。
Mendel cross-pollinated plants with different traits and carefully recorded the results. From his data, he deduced that traits are controlled by “factors” (now called genes) that come in pairs and are passed from parents to offspring.
孟德尔将具有不同性状的植物进行异花授粉，并仔细记录了结果。从数据中，他推断出性状是由成对出现的 “因子”（现在称为基因）控制的，这些因子由亲代传给子代。
He also proposed the Law of Segregation, which states that the two alleles for a trait separate during the formation of gametes (sex cells). This means each gamete carries only one allele for each gene. The Law of Independent Assortment states that alleles for different traits are distributed to gametes independently of one another.
他还提出了分离定律，即控制某一性状的两个等位基因在配子（性细胞）形成时彼此分离。这意味着每个配子只携带每个基因的一个等位基因。自由组合定律指出，不同性状的等位基因独立地分配到配子中。
6. Understanding Dominant and Recessive Traits | 理解显性与隐性性状
Mendel noticed that some traits seemed to disappear in the first generation of offspring but reappeared in the second generation. He called the trait that appeared in the first generation “dominant” and the one that was masked “recessive”. For example, in pea plants, tallness is dominant over shortness.
孟德尔注意到有些性状似乎在子一代中消失了，但在子二代中又重新出现。他把在子一代中出现的性状称为 “显性”，而被掩盖的性状称为 “隐性”。例如，在豌豆植物中，高茎对矮茎是显性的。
We now know that dominant alleles mask the effect of recessive alleles when both are present. A person with one dominant brown-eye allele and one recessive blue-eye allele will have brown eyes. To have blue eyes, a person must inherit two recessive alleles.
我们现在知道，当显性和隐性等位基因同时存在时，显性等位基因会掩盖隐性等位基因的作用。拥有一个显性棕色眼睛等位基因和一个隐性蓝色眼睛等位基因的人将会有棕色眼睛。要拥有蓝色眼睛，一个人必须继承两个隐性等位基因。
A Punnett square is a simple diagram used to predict the possible genetic outcomes of a cross. It shows all the possible combinations of alleles from the parents and the probability of each genotype.
庞纳特方格是一种简单的图表，用于预测杂交可能的遗传结果。它显示了来自父母的等位基因所有可能的组合以及每种基因型的概率。
7. Modern Genetic Experiments | 现代遗传实验
Since Mendel’s time, genetics has advanced dramatically. Scientists now use model organisms such as fruit flies (Drosophila), mice, and zebrafish to study gene function. These organisms share many genes with humans and can be easily manipulated in the laboratory.
自孟德尔时代以来，遗传学取得了巨大的进步。科学家现在使用模式生物，如果蝇（果蝇）、小鼠和斑马鱼来研究基因功能。这些生物与人类共享许多基因，并且很容易在实验室中进行操作。
One powerful technique is CRISPR-Cas9, which allows scientists to edit genes with great precision. By cutting DNA at a specific location, they can remove, add, or alter genetic material. This has opened up possibilities for treating genetic disorders and improving crop plants.
一种强大的技术是CRISPR-Cas9，它使科学家能够非常精确地编辑基因。通过在特定位置切割DNA，他们可以移除、添加或改变遗传物质。这为治疗遗传疾病和改良作物打开了可能性。
Another modern experiment is DNA sequencing, which determines the exact order of bases in a DNA molecule. The Human Genome Project, completed in 2003, mapped all the genes in human DNA. This has led to personalised medicine, where treatments can be tailored to an individual’s genetic makeup.
另一项现代实验是DNA测序，它确定DNA分子中碱基的精确顺序。于2003年完成的人类基因组计划绘制了人类DNA中所有基因的图谱。这导致了个性化医疗，即根据个人基因组成定制治疗方案。
8. Extracting DNA from Fruit | 从水果中提取DNA
You can see DNA with your own eyes by doing a simple experiment at home or in the classroom. One classic KS3 activity is extracting DNA from strawberries or bananas. These fruits are good choices because they have many copies of their chromosomes, making the DNA easier to collect.
你可以在家中或教室里做一个简单的实验，亲眼看到DNA。一种经典的KS3活动是从草莓或香蕉中提取DNA。这些水果是很好的选择，因为它们有多套染色体，使得DNA更容易收集。
To extract DNA, you first mash the fruit to break open the cells. Then you add a detergent solution, which dissolves the cell and nuclear membranes. After filtering the mixture, you add cold alcohol (such as ethanol) carefully down the side of the container. DNA is insoluble in alcohol, so it will appear as a white, stringy substance at the alcohol-water boundary.
要提取DNA，首先将水果捣碎以打破细胞。然后加入洗涤剂溶液，它会溶解细胞膜和核膜。过滤混合物后，沿着容器壁小心地加入冷酒精（如乙醇）。DNA不溶于酒精，因此它会在酒精-水界面处呈现白色丝状物质。
This experiment demonstrates that DNA is a physical molecule that can be isolated and observed. It also shows the importance of breaking cell structures to release the genetic material.
这个实验表明DNA是一种可以分离和观察的物理分子。它还显示了打破细胞结构以释放遗传物质的重要性。
9. Genetic Disorders and Testing | 遗传疾病与检测
Sometimes, a mutation in a gene can cause a genetic disorder. Examples include cystic fibrosis, sickle cell anaemia, and Down syndrome (which is caused by an extra copy of chromosome 21). These conditions are often inherited from one or both parents.
有时，基因突变会导致遗传疾病。例如囊性纤维化、镰状细胞贫血和唐氏综合征（由额外的一条21号染色体引起）。这些状况通常遗传自一方或双方父母。
Genetic testing can identify whether a person carries a faulty allele that might cause a disease. Prenatal testing can also detect certain genetic abnormalities in unborn babies. However, genetic testing raises important ethical questions about privacy, discrimination, and how
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