📚 Topic 3.3.2 Chromosomes, Genes and DNA | 主题3.3.2 染色体、基因与DNA
All living organisms carry a set of instructions that determine their characteristics, development and function. These instructions are passed from one generation to the next, forming the basis of heredity. In this article, we explore the core components of inheritance: chromosomes, genes and DNA, focusing on the IGCSE Edexcel Biology topic 3.3.2.
所有生物都携带着决定其性状、发育和功能的一套指令。这些指令代代相传，构成了遗传的基础。在本文中，我们将探讨遗传的核心组成部分：染色体、基因和DNA，重点对应IGCSE Edexcel生物学主题3.3.2的内容。
1. The Nucleus: Control Centre of the Cell | 细胞核：细胞的控制中心
In eukaryotic cells, the nucleus houses the cell's genetic material. It is surrounded by a nuclear envelope and contains chromatin, which condenses into visible chromosomes during cell division. The nucleus directs protein synthesis and cell reproduction by controlling gene expression.
在真核细胞中，细胞核储存着细胞的遗传物质。细胞核由核膜包围，内含染色质，在细胞分裂时染色质会凝聚成可见的染色体。细胞核通过控制基因表达来指导蛋白质合成与细胞繁殖。
Because the nucleus contains the instructions for building every protein, it is often described as the 'control centre' of the cell. Without a functional nucleus, a cell cannot coordinate its activities or divide properly.
由于细胞核含有合成所有蛋白质的指令，它常被形容为细胞的“控制中心”。缺少功能正常的细胞核，细胞便无法协调其活动或正常分裂。
2. Chromosomes: Carriers of Genetic Information | 染色体：遗传信息的载体
Chromosomes are thread-like structures composed of DNA and proteins. In human body (somatic) cells, there are 46 chromosomes arranged in 23 pairs. Each chromosome carries many genes. The number of chromosomes is characteristic of a species; for example, humans have 46, fruit flies have 8, and garden peas have 14.
染色体是由DNA和蛋白质组成的线状结构。在人体（体）细胞中，共有46条染色体，排列成23对。每条染色体携带众多基因。染色体的数目是物种的特征；例如，人类有46条，果蝇有8条，豌豆有14条。
| Species (物种) | Diploid chromosome number (2n) 二倍体染色体数 |
| Human (人类) | 46 |
| Fruit fly (果蝇) | 8 |
| Garden pea (豌豆) | 14 |
| Rice (水稻) | 24 |
| Cat (猫) | 38 |
In each pair, one chromosome is maternal and the other paternal. These matching pairs are called homologous chromosomes. They carry the same genes in the same order, although the versions (alleles) may differ.
每对染色体中，一条来自母亲，一条来自父亲。这些匹配的染色体叫做同源染色体。它们携带相同的基因且排列顺序一致，尽管这些基因的版本（等位基因）可能不同。
3. DNA: The Double Helix Molecule | DNA：双螺旋分子
Deoxyribonucleic acid (DNA) is a long polymer made of nucleotide subunits. Each nucleotide consists of a phosphate group, a deoxyribose sugar and a nitrogenous base. The four bases are adenine (A), thymine (T), cytosine (C) and guanine (G). The two DNA strands run in opposite directions and are held together by complementary base pairing: A always pairs with T, and C with G.
脱氧核糖核酸（DNA）是由核苷酸亚基组成的长链聚合物。每个核苷酸包含一个磷酸基团、一个脱氧核糖和一个含氮碱基。四种碱基分别是腺嘌呤（A）、胸腺嘧啶（T）、胞嘧啶（C）和鸟嘌呤（G）。两条DNA链走向相反，通过互补碱基配对结合在一起：A始终与T配对，C与G配对。
This double helix structure was discovered by Watson and Crick in 1953. The sequence of bases along a DNA strand encodes the instructions for building proteins, which determine the organism's traits.
这一双螺旋结构由沃森和克里克于1953年发现。DNA单链上的碱基序列编码着合成蛋白质的指令，而蛋白质决定着生物体的性状。
4. Genes: Units of Heredity | 基因：遗传单位
A gene is a specific sequence of DNA bases that codes for a particular protein. Genes are located on chromosomes at fixed positions called loci. The entire DNA of an organism is called its genome. Genes control characteristics such as eye colour, blood type and enzyme production. They are passed from parents to offspring through gametes during sexual reproduction.
基因是编码特定蛋白质的一段特定DNA碱基序列。基因位于染色体上被称为基因座的固定位置。一个生物体的全部DNA构成其基因组。基因控制着眼睛颜色、血型和酶的合成等性状。它们在有性生殖过程中通过配子从亲代传递给子代。
5. Alleles: Variations of a Gene | 等位基因：基因的变异形式
Genes can exist in different versions called alleles. For example, the gene for eye colour may have an allele for brown eyes and another for blue eyes. Alleles arise through mutations and are responsible for the variation observed within a species. A diploid organism carries two alleles for each gene, one inherited from each parent.
基因可以以不同的形式存在，这些形式称为等位基因。例如，控制眼睛颜色的基因可能有一个棕色眼等位基因，和一个蓝色眼等位基因。等位基因通过突变产生，是物种内出现变异的原因。二倍体生物每个基因携带两个等位基因，分别来自父母。
6. Genotype and Phenotype | 基因型和表现型
The genotype is
Published by TutorHao | IGCSE Biology Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
或截图后用「扫一扫 → 相册」选择本图