📚 Mendelian Inheritance: Key Concepts for CIE GCSE Biology | GCSE CIE 生物：孟德尔遗传 考点精讲
Mendelian inheritance describes the patterns by which genetic traits are passed from parents to offspring, based on the pioneering work of Gregor Mendel. For CIE GCSE Biology, you are expected to understand key terms such as alleles, dominant and recessive, homozygous and heterozygous, and be able to predict outcomes of monohybrid crosses using Punnett squares and interpret pedigree diagrams. This article covers all essential points in a clear, bilingual format.
孟德尔遗传描述了遗传性状从亲代传递给子代的方式，这一规律源于格里哥·孟德尔的开创性工作。在 CIE GCSE 生物考试中，你需要掌握等位基因、显性与隐性、纯合子与杂合子等关键术语，并能够运用庞纳特方格预测单基因杂交的结果、解读谱系图。本文将以清晰的中英双语形式梳理全部核心考点。
1. Mendel and His Pea Plants | 孟德尔与他的豌豆
Gregor Mendel, an Austrian monk, conducted experiments on garden pea plants (Pisum sativum) in the mid-19th century. He chose peas because they had several clearly contrasting traits, could self-pollinate or be cross-pollinated manually, and produced a large number of offspring in a short time.
孟德尔是一位奥地利修道士，在19世纪中期利用豌豆植物进行了遗传实验。他选择豌豆是因为它们具有多对对比鲜明的性状，可以自花授粉或人工异花授粉，并且能在短时间内产生大量后代。
Mendel studied seven characteristics, each with two distinct forms: stem height (tall or short), seed shape (round or wrinkled), seed colour (yellow or green), pod shape (inflated or constricted), pod colour (green or yellow), flower position (axial or terminal) and flower colour (purple or white). He started with pure-breeding lines for each trait.
孟德尔研究了七对相对性状，每对有两种截然不同的形式：茎高（高或矮）、种子形状（圆或皱）、种子颜色（黄或绿）、豆荚形状（饱满或皱缩）、豆荚颜色（绿或黄）、花的位置（腋生或顶生）以及花色（紫或白）。他首先确保每一性状的植株都是纯种。
When he crossed pure-breeding tall plants with pure-breeding short plants, all the first filial (F1) generation were tall. However, when the F1 plants were self-pollinated, the second filial (F2) generation showed both tall and short plants in an approximate ratio of 3:1. Mendel concluded that traits are not blended but determined by ‘factors’ (now called genes) that behave as discrete particles.
当他把纯种高茎与纯种矮茎杂交时，子一代（F1）全部表现为高茎。然而，让 F1 自花授粉后，子二代（F2）中同时出现了高茎和矮茎植株，比例约为 3:1。孟德尔由此推断，性状并非混合遗传，而是由“遗传因子”（现在称为基因）作为独立颗粒进行传递。
2. Key Genetic Terms | 关键遗传术语
A gene is a section of DNA that codes for a particular protein and determines a characteristic. Alleles are alternative versions of the same gene that occupy the same position (locus) on homologous chromosomes.
基因是编码特定蛋白质并决定某一性状的DNA片段。等位基因是同一基因的不同形式，它们位于同源染色体上的相同座位。
A diploid organism has two copies of each chromosome (one from each parent), so it possesses two alleles for each gene. These alleles may be identical or different. The combination of alleles is called the genotype, and the observable feature is the phenotype.
二倍体生物每种染色体都有两个拷贝（分别来自父本和母本），因此每个基因拥有两个等位基因。这对等位基因可能相同也可能不同。等位基因的组合称为基因型，而能观察到的特征称为表型。
A dominant allele is one that expresses itself in the phenotype even when only one copy is present. A recessive allele is only expressed when two copies are present (i.e. in the absence of the dominant allele).
显性等位基因是指即使只有一个拷贝也能在表型中表现出来的等位基因。隐性等位基因只有在两个拷贝都存在（即没有显性等位基因）时才能表达。
Homozygous means having two identical alleles for a trait (e.g. TT or tt). Heterozygous means having two different alleles (e.g. Tt). An organism that is heterozygous for a dominant trait will show the dominant phenotype.
纯合子指控制某一性状的两个等位基因相同（例如 TT 或 tt）。杂合子指两个等位基因不同（例如 Tt）。杂合子的个体在显性性状上仍表现显性表型。
3. Dominant and Recessive Alleles | 显性和隐性等位基因
In genetic crosses, dominant alleles are typically represented by an uppercase letter (e.g. T for tall), while recessive alleles use the lowercase form of the same letter (e.g. t for short). The same base letter is used because the alleles are variants of the same gene.
在遗传杂交中，显性等位基因通常用大写字母表示（如高茎 T），隐性等位基因用同一字母的小写形式（如 t）。使用相同字母是因为它们是同一基因的不同形式。
If a dominant allele is present, it masks the effect of the recessive allele. For example, a heterozygous plant with genotype Tt will be tall because the dominant T allele blocks the expression of the recessive t allele. The recessive allele can only show its effect in homozygous condition (tt).
只要显性等位基因存在，它就会掩盖隐性等位基因的作用。例如，基因型为 Tt 的杂合植株表现为高茎，因为显性 T 阻碍了隐性 t 的表达。隐性等位基因只有在纯合状态（tt）下才能显现。
4. Homozygous and Heterozygous | 纯合子和杂合子
True-breeding (pure-breeding) organisms are homozygous. For instance, a pure-breeding tall pea plant can be represented as TT, and a pure-breeding short plant as tt. Homozygous individuals produce only one type of gamete with respect to that gene.
纯种（真实遗传）生物是纯合的。例如，一株纯种高茎豌豆可表示为 TT，纯种矮茎为 tt。纯合个体针对该基因只产生一种类型的配子。
Heterozygous individuals (Tt) carry one dominant and one recessive allele. They produce two types of gametes in equal proportions: half carrying the dominant allele and half carrying the recessive allele. This is the basis of segregation predicted by Mendel’s First Law.
杂合个体（Tt）携带一个显性和一个隐性等位基因。它们产生两种类型的配子，且比例相等：一半携带显性等位基因，一半携带隐性等位基因。这正是孟德尔第一定律（分离定律）的基础。
5. Genotype and Phenotype | 基因型和表型
Genotype refers to the genetic constitution of an organism – the specific alleles it carries. Phenotype refers to the physical expression of those genes. The same phenotype can result from different genotypes; for example, both TT and Tt plants are tall.
基因型指生物的遗传组成，即它所携带的等位基因种类。表型则是这些基因的外在表现。相同的表型可能源自不同的基因型；例如 TT 和 Tt 植株都是高茎。
Phenotype can also be influenced by environmental factors, such as nutrition affecting height, but in Mendelian genetics, the focus is on traits largely determined by genotype. When predicting genetic outcomes, we always start with the genotypes of the parents.
表型也可能受环境因素影响，例如营养会影响身高，但在孟德尔遗传学中，重点关注主要由基因型决定的性状。在预测遗传结果时，我们总是从亲本的基因型开始分析。
6. Monohybrid Crosses | 单基因杂交
A monohybrid cross is a mating between individuals that differ in only one character controlled by a single pair of alleles. It allows us to track the inheritance of that single trait.
单基因杂交是指两个仅在一对等位基因控制的性状上存在差异的个体之间的交配。它帮助我们追踪单个性状的遗传规律。
Consider a cross between a homozygous dominant (TT) tall plant and a homozygous recessive (tt) short plant. All F1 offspring have the genotype Tt and are tall. When two F1 plants (Tt × Tt) are crossed, the F2 generation shows a genotypic ratio of 1 TT : 2 Tt : 1 tt and a phenotypic ratio of 3 tall : 1 short.
以纯合显性高茎 (TT) 与纯合隐性矮茎 (tt) 的杂交为例。F1 子代全部为 Tt，都是高茎。当两株 F1 植株（Tt × Tt）杂交时，F2 代的基因型比例为 1 TT : 2 Tt : 1 tt，表型比例为 3 高 : 1 矮。
Mendel’s law of segregation explains that the paired alleles separate during gamete formation so that each gamete receives only one allele. The random fusion of gametes at fertilisation restores the paired condition.
孟德尔分离定律指出，成对的等位基因在配子形成过程中彼此分离，因此每个配子仅含有一个等位基因。受精时配子随机结合，重新恢复成对状态。
7. Using Punnett Squares | 使用庞纳特方格
A Punnett square is a simple grid that helps predict the possible genotypes of offspring from a cross. The possible gametes of one parent are written along the top, and those of the other parent along the side. The boxes show the combinations of alleles at fertilisation.
庞纳特方格是一种简易的网格工具，用于预测杂交后代可能的基因型。将一方亲本可能的配子写在顶端，另一方写在侧边，方格内的组合即表示受精后的等位基因组合。
For a cross between two heterozygous tall plants (Tt × Tt), the gametes are T and t for each parent. The Punnett square produces genotypes TT, Tt, Tt and tt, confirming the 1:2:1 genotypic ratio and the 3:1 phenotypic ratio.
对于两株杂合高茎植株 (Tt × Tt) 的杂交，每方配子均为 T 或 t。庞纳特方格所得基因型为 TT、Tt、Tt 和 tt，恰好验证 1:2:1 的基因型比和 3:1 的表型比。
| Gametes | T | t |
| T | TT | Tt |
| t | Tt | tt |
It is essential in exams to correctly derive the gametes and fill the Punnett square systematically. Always state the expected ratios alongside the genotypes or phenotypes.
考试中务必正确推导配子类型，并条理清晰地填写庞纳特方格。务必在给出基因型或表型的同时写明预期比例。
8. Predicting Phenotypic Ratios | 预测表型比例
From a Punnett square, the phenotypic ratio for a monohybrid cross between two heterozygous individuals is typically 3 dominant : 1 recessive. A cross between a heterozygous and a homozygous recessive (test cross) yields a 1:1 ratio.
从庞纳特方格可以看出，两个杂合子之间的单基因杂交通常产生 3 显性 : 1 隐性的表型比。而杂合子与隐性纯合子（测交）则产生 1:1 的表型比。
A test cross is used to determine whether an organism showing a dominant trait is homozygous (TT) or heterozygous (Tt). The unknown organism is crossed with a homozygous recessive individual. If any recessive offspring appear, the unknown parent must be heterozygous.
测交通常用于鉴定显性性状个体是纯合子 (TT) 还是杂合子 (Tt)。将待测个体与隐性纯合子杂交。若后代出现隐性表型，则待测亲本必定为杂合子。
Ratios predicted by Punnett squares are probabilistic. In a small sample, actual numbers may deviate; however, over large numbers the expected ratios are observed.
庞纳特方格预测的比例是概率性的。样本较小时，实际数值可能有所偏差；但在大量统计下，预期比例是可以观察到的。
9. Codominance and Blood Groups | 共显性与血型
Codominance is a pattern of inheritance where both alleles in a heterozygous individual are fully expressed in the phenotype, rather than one masking the other. The result is a phenotype that shows both alleles simultaneously.
共显性是一种遗传模式，其杂合个体中的两个等位基因都能在表型中完全表达，而非一个掩盖另一个。结果表型同时展示两种等位基因的效应。
Human ABO blood groups provide a classic example. The gene for blood type has three alleles: IA, IB and i. Alleles IA and IB are codominant; both produce antigens on red blood cells. The i allele is recessive and produces no antigen.
人类 ABO 血型是经典的例子。血型基因具有三个等位基因：IA、IB 和 i。IA 与 IB 为共显性，两者都使红细胞表面产生抗原。i 等位基因为隐性，不产生抗原。
| Genotype |
Published by TutorHao | GCSE Biology Revision Series | aleveler.com 更多咨询请联系16621398022（同微信） CommentsMore posts |
屏轩国际教育cambridge primary/secondary checkpoint, cat4, ukiset,ukcat,igcse,alevel,PAT,STEP,MAT, ibdp,ap,ssat,sat,sat2课程辅导，国外大学本科硕士研究生博士课程论文辅导