英语周报七年级2019～202260期答案

23.(12分,除标注外,每空2分)(1)两(1分)两(1分)(2)AAbb1/4全为白花(3)①AAbb②杂交后代紫花:红花:白花=1:1:2【解析】(1)由表格可知,第1组中F2的表现型及比例为紫花:红花白花=9:3:4,是9:3:3:1的变形,所以该性状是由两对独立遗传的等位基因决定的,显性表现为紫色即只有在两种显性基因同时存在时丈能升紫花。(2)第1组中F1的紫花基因型为AaBb,红花亲本的基因型为aBB,则白花亲本的基因型为AAbb;F2白花基因型及比例为AAbb: Aabb: aabb=1:2:1,所以与白花亲本基因型相同的占1/4;同理第3组中F1的紫花基因型为AaBb,所以第3组中亲本白花的基因型为abb,第1组和第3组的白花亲本之间进行杂交,即 AAbbx aabb,后代基因型为Aabb,表现型全为白花。(3)第3组实验的F1为AaBb,纯合白花的基因型为AAbb或aabb。若该白花品种的基因型是AAbb,F1与纯合白花品种杂交,即AaBb×AAbb,子代基因型有四种,分别为AABb、AAbb、AaBb、Aabb,紫花与白花之比为1:1;若白花品种的基因型是abb,F1与纯合白花品种杂交,即AaBb×abb,子代的基因型有四种,分别为AaBb、Aabb、aBb、aabb,紫花:红花:白花=1:1:2。

Paragraph 1On Monday morning, hiding behind the window, wesoon saw what we were waiting for. It turned out that there They were too funny as they hopped away holding theirwere three of them from our school. They sneaked up on injured feet. We just couldn't contain our happiness andour snowman and sneered. Taking their places on either i excitement. With a hearty laugh, we came out of hidingside, they pulled back their legs to deliver powerful kicks. and sprang into the yard from inside the house. " An eye forBut the moment they hit the hard ice block of the base,. an eye! Justice done! "We yelled behind them. And thatsneers turned into shock, then agony and tears. They was the end of our problems with the snow bullies. Everhowled and cursed, gritting their teeth and stomping their i since then, our snowman was kept guarded and intact untilhappily melted into spring water and finally wove into ourParagraph 2sweetest childhood memoriesSeeing their pained looks, we couldn t help laughing

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