Inheritance: Genes, Alleles and Monohybrid Crosses | 遗传：基因、等位基因与单因子杂交

📚 Inheritance: Genes, Alleles and Monohybrid Crosses | 遗传：基因、等位基因与单因子杂交

Inheritance is the process by which genetic information is passed from one generation to the next. In the Edexcel IGCSE Biology specification, candidates are expected to understand the structure of genes and chromosomes, the meaning of key genetic terms, and the use of genetic diagrams to predict the outcomes of crosses. This article covers the essential knowledge needed for the exam, with worked examples and clear explanations in both English and Chinese.

遗传是指遗传信息从一代传递给下一代的过程。在 Edexcel IGCSE 生物考试大纲中，考生需要理解基因与染色体的结构、关键遗传术语的含义，以及运用遗传图解预测杂交结果。本文涵盖考试所需的核心知识，并配有双语例题与清晰讲解。

1. Chromosomes and Genes | 染色体与基因

In human body cells, the nucleus contains 23 pairs of chromosomes, making a total of 46 chromosomes. One chromosome from each pair comes from the mother and one from the father. Chromosomes are thread-like structures made of DNA and protein, and they are only visible during cell division when they condense into distinct shapes.

人体体细胞的细胞核中含有 23 对染色体，总共 46 条染色体。每对染色体中一条来自母亲，一条来自父亲。染色体是由 DNA 和蛋白质构成的线状结构，只有在细胞分裂时才会浓缩成清晰的形状，此时才容易被观察到。

A gene is a short section of DNA that codes for a specific protein or characteristic. Each chromosome carries many genes, and each gene occupies a fixed position called a locus (plural: loci). For example, the gene for hair colour is found at a particular locus on a particular chromosome.

基因是一小段 DNA，负责编码特定的蛋白质或性状。每条染色体上携带着许多基因，每个基因占据一个固定的位置，称为基因座（locus，复数为 loci）。例如，毛色基因位于某条染色体的特定基因座上。

• Humans have 23 pairs of chromosomes (46 in total). 人类有 23 对染色体（共 46 条）。
• Genes are sections of DNA that code for proteins. 基因是编码蛋白质的 DNA 片段。
• The position of a gene on a chromosome is called its locus. 基因在染色体上的位置称为基因座。

2. Alleles | 等位基因

Although a gene codes for one characteristic, that gene may exist in different forms. These different forms of the same gene are called alleles. For example, the gene for eye colour has one allele that codes for brown eyes and another allele that codes for blue eyes.

虽然一个基因编码一种性状，但同一个基因可以有不同的存在形式。同一基因的不同形式称为等位基因。例如，眼色基因有一个编码棕色眼睛的等位基因，也有一个编码蓝色眼睛的等位基因。

Because body cells contain pairs of chromosomes, they also contain pairs of alleles for each gene. One allele is inherited from the mother and one from the father. The two alleles may be identical or different, and their combination determines the characteristic that is expressed.

由于体细胞中含有成对的染色体，所以每个基因也有一对等位基因。一个等位基因来自母亲，另一个来自父亲。这两个等位基因可能相同，也可能不同，它们的组合决定了所表现出的性状。

3. Dominant and Recessive Alleles | 显性与隐性等位基因

In a pair of alleles, one may mask the effect of the other. The allele that is always expressed when present is called the dominant allele, and it is represented by a capital letter

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