📚 GCSE WJEC Biology: Meiosis Exam Tips | GCSE WJEC 生物：减数分裂考点精讲
Meiosis is a fundamental process for sexual reproduction, producing genetically unique gametes. Mastering this topic is essential for the WJEC GCSE Biology exam, as understanding chromosome behaviour during the two divisions explains how variation arises and why offspring resemble but are not identical to parents. This article breaks down every key stage, highlights common exam traps, and clarifies the vital differences between meiosis and mitosis.
减数分裂是有性生殖的基础过程，能够产生遗传上独一无二的配子。掌握这一主题对 WJEC GCSE 生物考试至关重要，因为理解两次分裂中染色体的行为能够解释变异如何产生、子代为何与亲代相似却不完全相同。本文将拆解每个关键阶段，点明常见考试陷阱，并清晰区分减数分裂与有丝分裂的重要差异。
1. What is Meiosis? | 什么是减数分裂？
Meiosis is a type of cell division that halves the chromosome number. A parent cell with the full diploid number (2n, 46 in humans) divides to produce four daughter cells, each with the haploid number (n, 23). These haploid cells are the gametes – sperm in males and egg cells in females. Without this reduction, fertilisation would double the chromosome number every generation.
减数分裂是一种使染色体数目减半的细胞分裂方式。一个拥有完整二倍体数目（2n，人类为46条）的亲代细胞分裂产生四个子细胞，每个子细胞只含单倍体数目（n，23条）。这些单倍体细胞就是配子——男性的精子和女性的卵细胞。如果没有这种减半作用，每一代受精都会导致染色体数目加倍。
In WJEC exams, you must be able to define meiosis as a reduction division. Remember that the chromosome number is halved, not the amount of DNA initially – after DNA replication the cell temporarily has 4n DNA content, but the diploid chromosome count is maintained until anaphase I.
在 WJEC 考试中，你必须能够将减数分裂定义为一种减数分裂。请记住，最初减半的是染色体数目，而不是 DNA 含量——DNA 复制后细胞暂时拥有 4n 的 DNA 含量，但二倍体染色体数一直维持到后期 I。
2. Where Does Meiosis Occur? | 减数分裂在哪里发生？
In animals, meiosis takes place only in the gonads. In males, it occurs in the testes to produce sperm; in females, it occurs in the ovaries to produce egg cells. In flowering plants, meiosis happens in the anthers (to form pollen grains) and in the ovules (to form embryo sacs). This restricted location is a common multiple‑choice question.
在动物中，减数分裂只发生在性腺里。雄性在睾丸中进行减数分裂以产生精子；雌性则在卵巢中进行以产生卵细胞。在开花植物中，减数分裂发生在花药（形成花粉粒）和胚珠（形成胚囊）中。这种特定的发生位置是常见的选择题考点。
Exam tip: WJEC often asks you to name the specific organs or structures. Expect a question like ‘Where does meiosis take place in a mammal?’ Always answer with testes or ovaries, not just ‘reproductive organs’.
应试提示：WJEC 经常要求你指出具体的器官或结构。可能会遇到“哺乳动物中减数分裂发生在哪里？”这样的问题。请务必回答睾丸或卵巢，而不是笼统地说“生殖器官”。
3. Before Meiosis: Interphase and DNA Replication | 减数分裂之前：间期与 DNA 复制
Just like mitosis, meiosis is preceded by interphase. During the S phase, each chromosome is replicated. After replication, every chromosome consists of two identical sister chromatids joined at a centromere. At this point the cell still has the diploid number of chromosomes, but double the DNA mass. The chromosomes are not yet visible under a light microscope – they remain as long, thin chromatin.
与有丝分裂一样，减数分裂之前是间期。在 S 期，每条染色体都进行复制。复制后，每条染色体由两条相同的姐妹染色单体组成，着丝粒将它们连接在一起。此时细胞仍然拥有二倍体数目的染色体，但 DNA 质量加倍。染色体在光学显微镜下仍不可见——它们还是细长的染色质。
Understanding this step helps you explain why meiosis II does not require another round of replication. WJEC may ask why there is no interphase II; the reason is that the DNA has already been duplicated.
理解这一步有助于解释为什么减数第二次分裂不需要再经历一轮复制。WJEC 可能会问为什么没有间期 II；原因是 DNA 在此之前已经完成复制。
4. Meiosis I – The Reduction Division | 减数第一次分裂——减数分裂
Meiosis I is called the reduction division because it is here that the chromosome number is halved. The homologous chromosomes pair up and then separate, with one chromosome from each pair going to each pole. The cell divides, producing two daughter cells that are haploid – each contains only one set of chromosomes, but each chromosome still consists of two sister chromatids.
减数第一次分裂被称为减数分裂，因为正是在此阶段染色体数目减半。同源染色体两两配对，然后分开，每一对中的一条染色体分别移向两极。细胞分裂后产生两个单倍体的子细胞——每个子细胞只含一套染色体，但每条染色体仍由两条姐妹染色单体组成。
Key concept: The reduction in chromosome number happens during anaphase I, not during meiosis II. Many students confuse this point, so make sure you associate the word ‘reduction’ firmly with meiosis I.
核心概念：染色体数目的减半发生在后期 I，而不是减数第二次分裂。许多学生在此处混淆，因此务必把“减数”一词牢固地与减数第一次分裂联系起来。
5. Prophase I: Homologous Pairing and Crossing Over | 前期 I：同源染色体配对与交叉互换
During prophase I, homologous chromosomes come together in a process called synapsis to form bivalents. Because each homologue has two chromatids, a bivalent is a structure of four chromatids. While they are paired, non‑sister chromatids may break and exchange corresponding segments of DNA – this is crossing over. The points where crossing over occurs are visible as chiasmata.
在前期 I，同源染色体通过联会过程聚集在一起，形成二价体。由于每条同源染色体都有两条染色单体，一个二价体就是一个由四条染色单体组成的结构。在配对的同时，非姐妹染色单体可能发生断裂并交换相应的 DNA 片段——这就是交叉互换。发生交叉互换的位置可见为交叉点（chiasmata）。
Crossing over creates new combinations of alleles on a chromosome. WJEC expects you to state that this is a major source of genetic variation. Be prepared to label a diagram showing a chiasma or to explain why offspring are genetically different from parents.
交叉互换在染色体上产生新的等位基因组合。WJEC 期望你指出这是遗传变异的主要来源。准备好在图中标出交叉点，或解释子代为何在遗传上不同于亲代。
6. Metaphase I: Independent Assortment | 中期 I：独立分配
In metaphase I, bivalents line up along the metaphase plate. The orientation of each bivalent is random – the maternal and paternal chromosomes can face either pole independently of the other pairs. This random arrangement is called independent assortment. It means that when the homologues separate, countless different combinations of maternal and paternal chromosomes can end up in the daughter cells.
在中期 I，二价体排列在赤道板上。每个二价体的朝向是随机的——母源和父源染色体可以独立地朝向任意一极，不受其他配对的影响。这种随机排列称为独立分配。这意味着当同源染色体分离时，母源和父源染色体的无数种不同组合都可能进入子细胞。
The formula for the number of possible combinations is 2n, where n is the haploid number. For humans (n=23), this gives over 8 million combinations from independent assortment alone. WJEC may ask you to calculate these combinations or simply to describe the process.
可能组合数的公式是 2n，n 为单倍体数目。对人来说（n=23），仅独立分配就能产生超过 800 万种组合。WJEC 可能会要求你计算这些组合，或仅描述该过程。
7. Anaphase I and Telophase I | 后期 I 与末期 I
During anaphase I, spindle fibres pull the homologous chromosomes apart. Unlike mitosis, the centromeres do not split; the sister chromatids remain attached. Whole chromosomes, each with two chromatids, move to opposite poles. This is the step that actually reduces the chromosome count from diploid to haploid. Telophase I then produces two new nuclei, usually followed by cytokinesis.
在后期 I，纺锤丝将同源染色体拉开。与有丝分裂不同的是，着丝粒并不分裂；姐妹染色单体仍连在一起。整条染色体（每条仍含两条染色单体）分别移向两极。正是这一步骤将染色体数目从二倍体减为单倍体。末期 I 随后形成两个新细胞核，通常紧接着胞质分裂。
Exam clarity: WJEC often uses diagrams of anaphase I. You must be able to identify that whole chromosomes are being separated, not chromatids. Look for the distinct shapes – each moving structure should have two chromatids if it is anaphase I.
考试明晰：WJEC 常会使用后期 I 的示意图。你必须能辨认出被分开的是整条染色体，而不是染色单体。观察形态——在后期 I 中，每个移动的结构应含有两条染色单体。
8. Meiosis II – Separation of Sister Chromatids | 减数第二次分裂——姐妹染色单体的分离
Meiosis II closely resembles mitosis, but the starting cells are haploid. There is no interphase II. In each of the two haploid cells, the chromosomes, still consisting of two chromatids, line up individually on the metaphase plate. The centromeres finally split during anaphase II, and the sister chromatids are pulled to opposite poles. Each chromatid becomes a separate chromosome in the new nuclei.
减数第二次分裂与有丝分裂非常相似，但起始细胞是单倍体。没有间期 II。在两个单倍体细胞中，仍由两条染色单体组成的染色体各自排列在赤道板上。着丝粒在后期 II 终于分裂，姐妹染色单体被拉向两极。每条染色单体在崭新的细胞核中成为一条独立的染色体。
Because the cells are already haploid, meiosis II simply separates the chromatids. WJEC may ask why meiosis II is not a reduction division. The answer is that the chromosome number remains haploid throughout; it does not halve again.
由于细胞已经是单倍体，减数第二次分裂只是分离染色单体。WJEC 可能会问为什么减数第二次分裂不是减数分裂。答案是整个过程中染色体数目保持单倍体不变，并没有再次减半。
9. Final Outcome: Four Haploid Cells | 最终结果：四个单倍体细胞
From one diploid parent cell, meiosis yields four haploid daughter cells. These cells are genetically different from each other and from the parent cell. In male animals, all four develop into functional sperm. In female animals, the cytoplasm divides unequally: one large egg cell and three small polar bodies that degenerate. In flowering plants, meiosis produces spores that develop into gametophytes.
由一个二倍体亲代细胞，减数分裂产生四个单倍体子细胞。这些细胞在遗传上彼此不同，也与亲代细胞不同。在雄性动物中，四个细胞全部发育为功能性精子。在雌性动物中，细胞质分配不均匀：形成一个大型卵细胞和三个退化的小极体。在开花植物中，减数分裂产生孢子，再由孢子发育成配子体。
Chromosome count summary: If the diploid number is 46, each gamete will have 23 chromosomes. Fertilisation restores the diploid number. WJEC often includes numerical problems, so practise stating the chromosome count after each stage.
染色体数目总结：如果二倍体数目是 46，每个配子将有 23 条染色体。受精作用使二倍体数目得以恢复。WJEC 经常包含数字计算题，因此要练习说出每个阶段后的染色体数目。
10. Sources of Genetic Variation | 遗传变异的来源
Meiosis generates genetic variation through two main mechanisms: crossing over during prophase I and independent assortment during metaphase I. Crossing over shuffles alleles between homologous chromosomes, producing new combinations on each chromatid. Independent assortment creates a mix of maternal and paternal chromosomes in each gamete. Additionally, the random fusion of gametes at fertilisation further amplifies variation.
减数分裂通过两个主要机制产生遗传变异：前期 I 的交叉互换和中期 I 的独立分配。交叉互换在同源染色体之间重排等位基因，在每条染色单体上产生新的组合。独立分配则在每个配子中产生母本和父本染色体的混合。此外，受精时配子的随机融合进一步放大了变异。
When WJEC asks you to ‘explain how meiosis causes variation’, you must mention both crossing over and independent assortment by name. Do not just say ‘the chromosomes mix’ – use the precise terms and describe the stages.
当 WJEC 要求你“解释减数分裂如何导致变异”时，你必须明确指出交叉互换和独立分配这两个名称。不要只说“染色体混合”——使用精确的术语并描述相应阶段。
11. Importance of Meiosis in Sexual Reproduction | 减数分裂在有性生殖中的重要性
Meiosis is crucial for sexual reproduction because it maintains a constant chromosome number across generations. If gametes were diploid, the chromosome number would double with each fertilisation. By halving the chromosome count, meiosis ensures that when two gametes fuse, the offspring inherits the correct diploid set. Furthermore, the variation produced by meiosis is the raw material for natural selection and evolution.
减数分裂对有性生殖至关重要，因为它维持了世代间恒定的染色体数目。如果配子是二倍体，每次受精染色体数目都会加倍。通过将染色体数目减半，减数分裂确保了当两个配子融合时，子代能够继承正确的二倍体染色体组。此外，减数分裂产生的变异为自然选择和进化提供了原材料。
WJEC may link this to the advantages of sexual reproduction. Be ready to explain that sexual reproduction produces variation within a population, whereas asexual reproduction typically produces genetically identical offspring.
WJEC 可能会将这一点与有性生殖的优势联系起来。请准备好解释：有性生殖能在种群内产生变异，而无性生殖通常产生遗传上完全相同的后代。
12. Comparing Meiosis and Mitosis | 比较减数分裂与有丝分裂
Mitosis produces two diploid daughter cells that are genetically identical to the parent cell and to each other. It involves one division and is used for growth, repair, and asexual reproduction. Meiosis produces four haploid daughter cells that are genetically unique. It involves two rounds of division and only occurs in gonads for gamete production. The behaviour of chromosomes in metaphase and anaphase is distinctly different.
有丝分裂产生两个二倍体子细胞，它们在遗传上与亲代细胞及彼此之间完全相同。它只涉及一次分裂，用于生长、修复和无性生殖。减数分裂产生四个遗传上独特的单倍体子细胞。它涉及两轮分裂，且仅在性腺中发生以产生配子。两者在中期和后期染色体的行为截然不同。
In the exam, comparison tables are common. Remember: mitosis keeps the chromosome number constant; meiosis halves it. Mitosis never includes pairing of homologues or crossing over, whereas meiosis does. These differences are high‑scoring WJEC marks if clearly stated.
考试中经常出现比较表格。请记住：有丝分裂保持染色体数目不变；减数分裂则将其减半。有丝分裂从不包含同源染色体配对或交叉互换，而减数分裂却包含这些。若能清晰陈述这些差异，就能在 WJEC 考试中拿到高分。
Published by TutorHao | Biology Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
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Cancel reply