🟢 遗传定律：孟德尔的豌豆密码🟢 Inheritance Laws: Mendel's pea code
上一片里，基因住在染色体这个"抽屉"里。可它怎么传给孩子？为什么有的特征会藏起来一代，又突然冒出来？答案在孟德尔的豌豆田里。Last leaf, genes were filed away in chromosome drawers. But how do they pass to children — and why can a trait vanish for a generation, then pop back? Mendel's pea patch has the answer.
第 1 步：高茎 × 矮茎，孩子全是高茎？Step 1: Tall × short — all tall?
先看小细胞亲手种的豌豆。First, look at the peas the little cell grew.
高茎豌豆和矮茎豌豆杂交，第一代孩子清一色是高茎，矮茎像被"吃掉"了；再让第一代互相杂交，第二代里矮茎又回来了——大约 3 高 : 1 矮。孟德尔数了上万株豌豆，才敢下这个结论。Cross a tall pea with a short one and the first generation comes out all tall — as if shortness was swallowed up. Let that generation cross again, and shortness returns: about 3 tall to 1 short. Mendel counted thousands of plants before daring to say so.
矮茎这一代，躲到哪儿去了？So where did the shortness hide?
第 2 步：显性的大 A，隐性的小 aStep 2: A dominant, a recessive
每个孩子从父母各拿一个基因版本。高茎版本是大 A（显性），矮茎版本是小 a（隐性）。有 A 就长高；只有 aa 两个小 a 碰头，才长矮。第一代都拿着 Aa——藏着矮茎的秘密，外表却是高茎。遗传不是混合颜料，它传的是一张张完整的字母卡。Every child takes one version of the gene from each parent. Tall comes as big A (dominant), short as little a (recessive). One A is enough to grow tall; only two little a's together grow short. The first generation all carry Aa — hiding shortness while looking tall. Inheritance is not mixing paint: it passes whole letter cards along.
那 Aa 和 Aa 的孩子，会是什么样？So what do the children of Aa and Aa look like?
第 3 步：抽卡片定比例Step 3: Draw cards, set the odds
把双方的两张卡各随机抽一张来配：AA、Aa、aA、aa 各占 1/4。前三组都有大 A，都是高茎——所以每个孩子约 3/4 高、1/4 矮。每次生育都是一次新的抽卡，上一个孩子是矮茎，也不会让下一个更高或更矮。Draw one card from each parent at random: AA, Aa, aA and aa are each equally likely. The first three all carry a big A and grow tall — so each child has roughly a 3-in-4 chance of being tall, 1-in-4 short. Every child is a fresh draw: a short first child never biases the next.
🎮 你来种豌豆（30 秒）🎮 Your turn: plant some peas (30 seconds)
道理讲完了。点基因卡换亲本，盯着 4 个后代的方格和比例，再完成 4 个配种任务。Theory done. Tap the gene cards to switch parents, watch the 4 offspring squares and the ratio, then finish 4 breeding tasks.
一句话记住它：基因像两张字母卡，孩子从父母各抽一张；有显性大 A 就露 A 的样子，两个隐性小 a 碰头才露小 a。Remember it in one line: genes are letter cards — each child draws one from each parent; a dominant A shows itself, and only two recessive a's reveal a's look.
显性（大 A）盖住隐性（小 a）；隐性没消失，只是藏起来了Dominant (big A) masks recessive (little a): hidden, not gone孟德尔豌豆：高 × 矮 → 第一代全高 → 第二代 3 : 1Mendel's peas: tall × short → all tall → then 3 : 1遗传是"抽卡片"：每胎独立，约 3/4 高、1/4 矮，不是混合平均Inheritance is drawing cards: each child is an independent 3/4-tall, 1/4-short draw — never a blend
内容参考 OpenStax 等公开教材，多来源核对 · AI 生成、人工审核 · 发现错误欢迎指正，帮这片叶子长得更好。Based on OpenStax and other open textbooks, cross-checked across sources · AI-generated, human-reviewed · Spotted a mistake? Tell us — help this leaf grow.
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