📚 Inheriting Genes | 基因的遗传
Inheritance is the passage of genetic information from one generation to the next. In A-Level Biology, this topic explains how alleles segregate and assort, producing characteristic phenotypic ratios such as 3:1, 1:1 and 9:3:3:1.
遗传是遗传信息从一代传递给下一代的过程。在A-Level生物中，本主题解释等位基因如何分离和分配，从而产生特征性的表型比例，如3:1、1:1和9:3:3:1。
Understanding the language of genetics, monohybrid and dihybrid crosses, sex linkage, epistasis and statistical testing is essential for solving inheritance problems accurately.
理解遗传学术语、单基因和双基因杂交、性连锁、上位效应以及统计检验，对于准确解决遗传学问题至关重要。
1. Genetic Terminology | 遗传学术语
The basic unit of inheritance is the gene, a DNA sequence that codes for a polypeptide or functional RNA. Each gene occupies a specific locus on a chromosome.
遗传的基本单位是基因，即编码多肽或功能RNA的DNA序列。每个基因在染色体上占据特定的基因座。
Diploid organisms have homologous pairs of chromosomes, so each cell carries two copies of each gene. These copies are called alleles and may be identical or different.
二倍体生物具有成对的同源染色体，因此每个细胞携带每个基因的两个拷贝。这些拷贝称为等位基因，可以相同也可以不同。
A dominant allele is expressed in the phenotype even when only one copy is present, whereas a recessive allele is only expressed when two copies are present. Homozygous individuals have two identical alleles at a locus, while heterozygous individuals have two different alleles.
显性等位基因即使只有一个拷贝也会在表型中表达，而隐性等位基因只有在两个拷贝都存在时才表达。纯合个体在一个基因座上有两个相同等位基因，而杂合个体有两个不同等位基因。
The genotype is the genetic constitution of an individual, while the phenotype is the observable characteristic produced by the genotype and the environment.
基因型是个体的遗传组成，而表型是基因型和环境共同产生的可观察特征。
2. Monohybrid Inheritance | 单基因杂交遗传
In a monohybrid cross, two pure-breeding parents differing in one characteristic are crossed. For example, a homozygous tall plant (TT) is crossed with a homozygous dwarf plant (tt).
在单基因杂交中，两个在一个性状上不同的纯种亲本进行杂交。例如，纯合高茎植株（TT）与纯合矮茎植株（tt）杂交。
Each parent produces gametes carrying one allele only, so the F₁ generation is all Tt and shows the tall phenotype. When the F₁ plants self-pollinate, they produce gametes T and t in equal numbers.
每个亲本只产生携带一个等位基因的配子，因此F₁代全为Tt，并表现为高茎。当F₁植株自交时，它们产生数量相等的T和t配子。
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