GCSE CCEA Biology: Mendelian Genetics Revision | GCSE CCEA 生物：孟德尔遗传考点精讲

📚 GCSE CCEA Biology: Mendelian Genetics Revision | GCSE CCEA 生物：孟德尔遗传考点精讲

Mendelian genetics forms the cornerstone of inheritance studies in GCSE CCEA Biology. Understanding how characteristics are passed from parents to offspring through discrete units called genes is essential for answering exam questions on monohybrid and dihybrid crosses, pedigree analysis, and genetic disorders.

孟德尔遗传是 GCSE CCEA 生物学中遗传学研究的基石。理解特征如何通过称为基因的离散单位从亲代传递给子代，对于回答单基因杂交、双基因杂交、系谱分析以及遗传疾病等问题至关重要。

1. Introduction to Mendel and His Pea Plants | 孟德尔与他的豌豆植株简介

Gregor Mendel, an Austrian monk, conducted groundbreaking experiments on garden peas (Pisum sativum) in the mid-19th century. He chose pea plants because they have several distinct contrasting traits, reproduce quickly, and can be self-pollinated or cross-pollinated.

格雷戈尔·孟德尔，一位奥地利修道士，在19世纪中期对豌豆（Pisum sativum）进行了开创性实验。他选择豌豆是因为它们具有多种鲜明的相对性状、繁殖速度快，并且可以自花传粉或异花传粉。

Mendel tracked seven characteristics including seed shape (round vs. wrinkled), seed colour (yellow vs. green), and plant height (tall vs. dwarf). His quantitative approach allowed him to deduce the fundamental laws of inheritance.

孟德尔追踪了七个特征，包括种子形状（圆粒与皱粒）、种子颜色（黄色与绿色）以及植株高度（高茎与矮茎）。他的定量研究方法使他推断出遗传的基本定律。

2. Key Genetic Terms | 关键遗传学术语

Before tackling genetic crosses, you must be fluent in the following terminology:

在解决遗传杂交问题之前，你必须熟练下列术语：

Gene – A section of DNA that codes for a particular protein, determining a trait.

基因 – 编码特定蛋白质的一段 DNA，决定某个性状。

Allele – Different forms of the same gene. For example, the gene for plant height has an allele for tall (T) and an allele for dwarf (t).

等位基因 – 同一基因的不同形式。例如，植株高度基因有高茎等位基因 (T) 和矮茎等位基因 (t)。

Dominant allele – An allele that is always expressed in the phenotype when present. Represented by a capital letter (e.g., T for tall).

显性等位基因 – 存在时总在表现型中表达的等位基因。用大写字母表示（如高茎用 T）。

Recessive allele – An allele that is only expressed when no dominant allele is present. Represented by a lowercase letter (e.g., t for dwarf).

隐性等位基因 – 只有在没有显性等位基因存在时才表达的等位基因。用小写字母表示（如矮茎用 t）。

Homozygous – Having two identical alleles for a gene (e.g., TT or tt). Also called pure-breeding.

纯合子 – 对于某个基因有两个相同等位基因（如 TT 或 tt）。也称为纯种。

Heterozygous – Having two different alleles for a gene (e.g., Tt). Also called a hybrid or carrier for a recessive trait.

杂合子 – 对于某个基因有两个不同等位基因（如 Tt）。也称为杂种或隐性性状的携带者。

Genotype – The genetic makeup of an organism (e.g., TT, Tt, tt).

基因型 – 生物体的基因组成（如 TT、Tt、tt）。

Phenotype – The observable physical or biochemical characteristic (e.g., tall or dwarf).

表现型 – 可观察的物理或生化特征（如高茎或矮茎）。

3. Monohybrid Inheritance and the Law of Segregation | 单基因遗传与分离定律

Mendel’s Law of Segregation states that each individual possesses two alleles for each gene, but only one allele is passed into each gamete. The pairs of alleles separate (segregate) during gamete formation (meiosis).

孟德尔分离定律指出，每个个体对于每个基因拥有两个等位基因，但在形成配子时仅有一个等位基因进入配子。等位基因对在配子形成（减数分裂）期间分离（分离）。

In a monohybrid cross, parents differing in a single characteristic are crossed. For example, a homozygous dominant tall plant (TT) crossed with a homozygous recessive dwarf plant (tt) produces F₁ offspring that are all heterozygous (Tt) and tall, because the dominant allele masks the recessive one.

在单基因杂交中，将对单一特征有差异的亲本进行杂交。例如，一个纯合显性高茎植株 (TT) 与一个纯合隐性矮茎植株 (tt) 杂交，产生的 F₁ 后代全部

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