1. 遗传学导论 · Introduction to Genetics
遗传学研究基因如何从亲代传给子代。OCR GCSE Biology大纲（J247）将遗传学分为三个层次：分子基础（DNA、蛋白质合成）、遗传规律（孟德尔遗传）、进化与应用（自然选择、基因工程）。
Genetics studies how genes pass from parents to offspring. The OCR GCSE Biology specification (J247) divides genetics into three tiers: molecular foundation (DNA, protein synthesis), inheritance patterns (Mendelian genetics), and evolution and applications (natural selection, genetic engineering).
2. DNA结构与功能 · DNA Structure and Function
DNA是双螺旋结构：磷酸-脱氧核糖主链通过碱基对以氢键相连。互补配对原则是必考点：A-T，C-G。核苷酸是基本单位，基因是编码蛋白质的DNA片段，基因组是全部遗传物质。
DNA has a double helix structure: sugar-phosphate backbones linked by base pairs via hydrogen bonds. Complementary base pairing is guaranteed on the exam: A-T, C-G. A nucleotide is the basic unit, a gene codes for a protein, and the genome is all genetic material.
3. 蛋白质合成 · Protein Synthesis
转录在细胞核进行：DNA作模板合成mRNA（T被U替代）。翻译在核糖体进行：每三个碱基（密码子）对应一个氨基酸，tRNA携带氨基酸配对连接成多肽链，折叠成蛋白质。
Transcription in the nucleus: DNA as template produces mRNA (T replaced by U). Translation on ribosomes: every three bases (codon) match one amino acid; tRNA carries amino acids to form a polypeptide chain that folds into a protein.
4. 孟德尔遗传与单基因杂交 · Mendelian Genetics and Monohybrid Crosses
等位基因是同一基因的不同版本。显性（大写，如B）只需一个拷贝即表达；隐性（小写，如b）需两个拷贝。基因型（BB/Bb/bb）vs 表现型（实际性状）。纯合（BB或bb）vs 杂合（Bb）。
An allele is a different version of a gene. Dominant (capital letter, e.g. B) needs one copy; recessive (lowercase, e.g. b) needs two. Genotype (BB/Bb/bb) vs phenotype (actual trait). Homozygous (BB or bb) vs heterozygous (Bb).
5. 庞纳特方格 · Punnett Squares
Bb × Bb杂交：基因型比1BB:2Bb:1bb，显性表现型比3:1。务必标注亲代配子于方格边缘。家系图中圆圈=女性，方框=男性，实心=表达性状。
Bb x Bb cross: genotype ratio 1BB:2Bb:1bb, dominant phenotype ratio 3:1. Always label parental gametes on grid edges. Pedigree charts: circle=female, square=male, filled=expresses trait.
6. 遗传病 · Genetic Disorders
囊性纤维化（隐性，ff患病，Ff为携带者）：影响氯离子通道，黏液阻塞肺部和消化系统。多指症（显性，一个P即患病）：患者有多余指/趾，患病父母传给子女的概率为50%。
Cystic Fibrosis (recessive, ff=affected, Ff=carrier): affects chloride channels, mucus blocks lungs and digestion. Polydactyly (dominant, one P=affected): extra fingers/toes; 50% chance of inheritance from an affected parent.
7. 突变与变异 · Mutations and Variation
突变是DNA序列的随机改变，由辐射、化学物质或复制错误引起。遗传变异（基因差异，可遗传）vs 环境变异（外部因素，不可遗传）。OCR常要求区分两者类型。
Mutations are random DNA changes from radiation, chemicals, or replication errors. Genetic variation (gene differences, heritable) vs environmental variation (external factors, not heritable). OCR frequently asks to classify trait types.
8. 自然选择与进化 · Natural Selection and Evolution
达尔文理论：种群内存在遗传变异 → 环境选择压力 → 有利性状个体存活繁殖 → 有利等位基因增多 → 物种进化。经典考题：抗生素耐药菌——变异预先存在，抗生素杀死敏感菌，耐药菌繁殖成为主流。华莱士独立提出相似理论。
Darwin's theory: genetic variation exists → selection pressure → advantageous traits survive and reproduce → advantageous alleles increase → evolution. Classic exam question: antibiotic-resistant bacteria — variation pre-exists, antibiotics kill sensitive bacteria, resistant ones become dominant. Wallace independently proposed a similar theory.
9. 选择性育种与基因工程 · Selective Breeding and Genetic Engineering
选择性育种：选理想性状个体交配，多代获得稳定品系（如高产奶牛），但减少遗传多样性。基因工程：限制酶切基因 → 连接酶插入载体（质粒）→ 导入宿主 → 表达目标蛋白（如细菌产胰岛素）。
Selective breeding: mate individuals with desirable traits over generations (e.g. high-yield cows), but reduces genetic diversity. Genetic engineering: restriction enzymes cut gene → ligase inserts into vector (plasmid) → introduced into host → expresses target protein (e.g. bacteria producing insulin).
10. 考试策略 · Exam Strategy
高频考点：碱基配对规则、转录翻译步骤、庞纳特方格计算、囊性纤维化vs多指症对比、自然选择六分题。常见失分：混淆基因与等位基因、mRNA写T不写U、自然选择漏写"变异预先存在"。六分题使用QWC策略，逻辑清晰并用精准术语。
High-frequency topics: base pairing rules, transcription and translation steps, Punnett Square calculations, Cystic Fibrosis vs Polydactyly comparison, natural selection 6-mark questions. Common pitfalls: confusing gene vs allele, writing T instead of U in mRNA, omitting "variation pre-exists" in natural selection. For 6-mark questions, use QWC strategy with clear logic and precise terminology.
遗传学是OCR GCSE Biology的高分模块，掌握分子机制与遗传规律，6分题不再是难题。
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