化石是最有说服力的生物进化证据。化石记录显示：形成早的古老地层中，化石生物的种类 ____，结构 ____．

（2015$·$浙江）某自花且闭花授粉植物， 抗病性和茎的高度是独立遗传的性状。 抗病和感病由基因 R 和 r 控制， 抗病为显性； 茎的高度由两对独立遗传的基因（ D 、 d ， E 、 e ） 控制， 同时含有 D 和 E 表现为矮茎， 只含有 D 或 E 表现为中茎， 其他表现为高茎。 现有感病矮茎和抗病高茎两品种的纯合种子， 欲培育纯合的抗病矮茎品种。。

请回答：

（ 1 ） 自然状态下该植物一般都是 _______ 合子。____ 

（ 2 ） 若采用诱变育种， 在γ 射线处理时， 需要处理大量种子， 其原因是基因突变具有 ______和有害性这三个特点。____ 

（ 3 ） 若采用杂交育种， 可通过将上述两个亲本杂交， 在 F₂等分离世代中 _____ 抗病矮茎个体， 再经连续自交等 _____ 手段， 最后得到稳定遗传的抗病矮茎品种。 据此推测， 一般情况下， 控制性状的基因数越多， 其育种过程所需的 _____ 。 若只考虑茎的高度， 亲本杂交所得的 F₁ 在自然状态下繁殖， 则理论上， F₂的表现型及比例为 _______ 。____ 

（ 4 ） 若采用单倍体育种， 该过程涉及的原理有 ____ 。 请用遗传图解表示其过程（说明： 选育结果只需写出所选育品种的基因型、 表现型及其比例）。____ 

    “Get up, get up, Jim. It's time to get up!” My mother said while she was pushing me. I opened my eyes and looked at the clock. “Oh dear! It's a quarter past eight already.” I'll be late for school again,” I thought. I jumped out of the bed, washed my face, and then hurried to the bus stop without breakfast. As soon as I   got on the bus, it started running. “I'm sure I can get to school in time,” I said to myself. Suddenly the bus stopped. The bus driver got off the bus, then got on the bus again and said, “I'm sorry, ladies and gentlemen. There's something wrong with the bus. Please get off the bus and wait for another one.” “I couldn't wait. The school isn't far. I'd better run to school,” I thought, and then I began to run. But before I got to school, it began to rain hard.

    I reached the classroom but I was wet shivering with cold. The math teacher had already begun his lesson. It was Mr. Smith. He was very strict with his students and the students were a little afraid of him and so was I. I liked neither him nor his math lessons. I hesitated (犹豫) for a moment, and then I opened the door. “I'm very sorry, Mr. Smith. I'm late again,” I said with a red face.

    “It's you again, Jim,” Mr. Smith said angrily, “I've told you not to be late, but you...” he suddenly stopped and looked at my wet clothes. He turned to   the class and said, “I'm very sorry, boys and girls. ” With these words he quickly took off his own jacket and handed it to me. “Now, take off your wet coat and put on this one or you'll catch cold,” he said kindly.

    I went to my seat with Mr. Smith's jacket on. It was a bit larger for me but I felt very warm in it. I found, for the first time, math was so interesting and how well I could understand it!

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