📚 Dihybrid Crosses and the Laws of Inheritance | 双因子杂交实验与遗传规律
In A-Level Biology, the dihybrid cross is one of the most important tools for understanding how two different characters are inherited at the same time. It provides direct evidence for Mendel’s law of independent assortment.
在 A-Level 生物中，双因子杂交是理解两个不同性状如何同时遗传的最重要工具之一。它直接验证了孟德尔的独立分配定律（自由组合定律）。
1. What is a Dihybrid Cross? | 什么是双因子杂交？
In a dihybrid cross, two characters are followed simultaneously. For example, in peas, seed shape (round or wrinkled) and seed colour (yellow or green) are controlled by two different genes.
在双因子杂交中，同时跟踪两个性状。例如，在豌豆中，种子形状（圆形或皱缩）和种子颜色（黄色或绿色）由两对不同的基因控制。
We use one letter for each gene. The allele for round seeds is represented by R and the allele for wrinkled seeds by r; the allele for yellow seeds is represented by Y and the allele for green seeds by y.
我们用字母代表每对基因。圆形种子的等位基因用 R 表示，皱缩种子的等位基因用 r 表示；黄色种子的等位基因用 Y 表示，绿色种子的等位基因用 y 表示。
Round and yellow are dominant because the phenotypes appear when at least one dominant allele is present.
圆形和黄色是显性性状，因为只要存在至少一个显性等位基因，这些表型就会出现。
2. Mendel’s Dihy
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