GCSE Edexcel Science: Genetics Key Points | GCSE Edexcel 科学：遗传 考点精讲

📚 GCSE Edexcel Science: Genetics Key Points | GCSE Edexcel 科学：遗传 考点精讲

Genetics is a core topic in GCSE Edexcel Science, exploring how traits are inherited from one generation to the next. This article covers the essential concepts, from DNA structure to Mendelian inheritance, monohybrid crosses, pedigrees, and more, providing a bilingual revision guide for Chinese-speaking students.

遗传是 GCSE Edexcel 科学中的核心主题，探索性状如何代代相传。本文涵盖从 DNA 结构到孟德尔遗传、单基因杂交、家系图等关键概念，为中文学生提供双语复习指南。

1. DNA, Genes and Chromosomes | DNA、基因与染色体

DNA (deoxyribonucleic acid) is a double helix polymer made of nucleotides. Each nucleotide contains a sugar, a phosphate group, and a nitrogenous base (A, T, C, or G).

DNA（脱氧核糖核酸）是一种双螺旋聚合物，由核苷酸组成。每个核苷酸包含一个糖、一个磷酸基团和一个含氮碱基（A、T、C 或 G）。

Base pairing rules: adenine (A) pairs with thymine (T), and cytosine (C) pairs with guanine (G).

碱基配对规则：腺嘌呤（A）与胸腺嘧啶（T）配对，胞嘧啶（C）与鸟嘌呤（G）配对。

A gene is a short section of DNA that codes for a specific protein. Genes determine our characteristics.

基因是编码特定蛋白质的一小段 DNA。基因决定了我们的性状。

Chromosomes are long, coiled molecules of DNA found in the nucleus. Humans have 46 chromosomes arranged in 23 pairs, one set from each parent.

染色体是位于细胞核内的长链、卷曲的 DNA 分子。人类有 46 条染色体，排成 23 对，分别来自父母。

2. Alleles and Genetic Terms | 等位基因与遗传术语

An allele is a different version of the same gene. For example, the gene for eye colour has alleles for blue, brown, etc.

等位基因是同一基因的不同版本。例如，眼睛颜色的基因有蓝色、棕色等等位基因。

A dominant allele is always expressed in the phenotype even if only one copy is present. A recessive allele is only expressed when two copies are present (homozygous recessive).

显性等位基因只要存在一个拷贝即可在表型中表达。隐性等位基因只有在存在两个拷贝时才能表达（隐性纯合）。

Homozygous means having two identical alleles for a gene (e.g., BB or bb). Heterozygous means having two different alleles (e.g., Bb).

纯合子指某基因有两个相同的等位基因（如 BB 或 bb）。杂合子指有两个不同的等位基因（如 Bb）。

Genotype is the genetic makeup of an organism (alleles present). Phenotype is the observable characteristic, influenced by genotype and environment.

基因型是生物体的遗传组成（拥有的等位基因）。表型是可观察到的特征，受基因型和环境影响。

3. Monohybrid Inheritance and Punnett Squares | 单基因遗传与庞纳特方格

Monohybrid inheritance is the inheritance of a single characteristic controlled by one gene with two alleles. Gregor Mendel discovered the basic patterns through pea plant experiments.

单基因遗传是指由一对等位基因控制一个性状的遗传。格雷戈尔·孟德尔通过豌豆实验发现了基本遗传模式。

Consider a cross between a homozygous dominant tall plant (TT) and a homozygous recessive short plant (tt). The F1 generation is all heterozygous tall (Tt).

考虑纯合显性高茎植株（TT）与纯合隐性矮茎植株（tt）杂交。F1 代全部为杂合高茎（Tt）。

When two F1 plants (Tt) are crossed, the offspring show a 3:1 phenotypic ratio. A Punnett square predicts the genotypes.

当两株 F1 植株（Tt）杂交时，后代表现 3:1 的表型比。庞纳特方格可以预测基因型。

Genotypic ratio: 1 TT : 2 Tt : 1 tt. Phenotypic ratio: 3 tall : 1 short.

基因型比：1 TT : 2 Tt : 1 tt。表型比：3 高茎 : 1 矮茎。

The probability of an offspring inheriting a certain genotype can be given as a fraction or percentage. For example, in this cross, there is a

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