📚 IB CIE Science: Genetics Essentials | IB CIE 科学：遗传 考点精讲
Genetics is the branch of biology that explains how traits are passed from parents to offspring through genes. Understanding key concepts such as alleles, Mendel’s laws, inheritance patterns, mutations, and genetic technologies is essential for success in both IB and CIE science examinations. This article summarises the core topics you must master, with clear bilingual explanations.
遗传学是生物学的一个分支，解释性状如何通过基因从亲代传递给子代。掌握等位基因、孟德尔定律、遗传模式、突变和基因技术等关键概念，对于在 IB 和 CIE 科学考试中取得成功至关重要。本文总结了你必须掌握的核心主题，并配有清晰的双语说明。
1. Genes, Chromosomes and DNA | 基因、染色体与DNA
A gene is a segment of DNA that codes for a specific protein or functional RNA. Genes are located on chromosomes, which are long DNA molecules wrapped around histone proteins. In eukaryotes, chromosomes are found in the nucleus. Each gene occupies a specific locus on a chromosome.
基因是编码特定蛋白质或功能RNA的DNA片段。基因位于染色体上，染色体是缠绕在组蛋白上的长DNA分子。在真核生物中，染色体存在于细胞核内。每个基因在染色体上占据特定的基因座。
DNA has a double helix structure with a sugar-phosphate backbone and nitrogenous bases (adenine, thymine, cytosine, guanine). The sequence of bases determines the genetic code. Alleles are different versions of the same gene that arise due to small differences in the DNA sequence.
DNA具有双螺旋结构，由糖-磷酸骨架和含氮碱基（腺嘌呤、胸腺嘧啶、胞嘧啶、鸟嘌呤）组成。碱基序列决定遗传密码。等位基因是同一基因的不同版本，它们因DNA序列的微小差异而产生。
2. Alleles, Genotype and Phenotype | 等位基因、基因型与表现型
An allele is one of two or more alternative forms of a gene. A diploid organism inherits two alleles for each gene, one from each parent. If the two alleles are identical, the individual is homozygous; if different, heterozygous. The genotype is the combination of alleles present, while the phenotype is the observable characteristic resulting from the genotype and environmental influences.
等位基因是基因的两种或多种替代形式之一。二倍体生物的每个基因继承两个等位基因，分别来自父母。如果两个等位基因相同，个体是纯合的；如果不同，则是杂合的。基因型是存在的等位基因组合，而表现型是由基因型与环境影响共同产生的可观察特征。
Dominant alleles mask the effect of recessive alleles in heterozygotes. For example, in pea plants, the allele for tall stem (T) is dominant over the allele for short stem (t). Only one dominant allele is needed for the dominant trait to be expressed.
显性等位基因在杂合子中掩盖隐性等位基因的效应。例如，在豌豆植株中，高茎等位基因（T）对矮茎等位基因（t）呈显性。只需一个显性等位基因，显性性状就能表达。
3. Mendel’s Laws: Segregation and Independent Assortment | 孟德尔定律：分离与自由组合
Gregor Mendel established two fundamental laws of inheritance. The Law of Segregation states that during gamete formation, the two alleles for a gene separate so that each gamete carries only one allele. This explains the 3:1 phenotypic ratio in the F2 generation of a monohybrid cross.
格雷戈尔·孟德尔建立了两个基本的遗传定律。分离定律指出，在配子形成过程中，一个基因的两个等位基因分离，使得每个配子只携带一个等位基因。这解释了单因子杂交F2代中3:1的表现型比例。
The Law of Independent Assortment states that alleles of different genes assort independently of one another during gamete formation, provided the genes are on different chromosomes or far apart on the same chromosome. This leads to the 9:3:3:1 phenotypic ratio in a dihybrid cross.
Published by TutorHao | IB Science Revision Series | aleveler.com更多咨询请联系16621398022（同微信）
或截图后用「扫一扫 → 相册」选择本图