2022英语周报七年级新目标YYY答案

第一节Dear Mr GeorgeI am Li Hua, a volunteer of the activity"Englishi Communication to the Mountains". Now, I'm writing toexpress my sincere apology to you for not being present atthe activity to be held next Monday.The reason for my absence is that I suddenly fell illMy parents sent me to hospital, and I have to stay therefor a week. As for my volunteer work, I have asked myclassmate Tom to do it.Sincerely hoping that you can accept my apologiesYours.Li Hua

21.(14分,每空2分)(1)黄色、灰色(2)Aa2、a1a21/8(3)6(4)实验思路黑结果预测:①Aa1②黄色和黑色【解析】(1)若亲本基因型为Aa1×Aa2,则子代的基因型为1AA、1Aa1、1Aa2、1a1a2,AA纯合胚胎致死,子代表现型为黄色、灰色。(2)两只鼠杂交,后代出现三种表现型,其中包括黑色a2a2,说明双亲均含有a2基因,且一个亲本含有A基因,一个亲本含有a1基因,则该对亲本的基因型是Aa2、B2a2,它们再生一只黑色雄鼠的率(1/4)×(1/2)=1/8。(3)假设进行很多Aa2×a2的杂交,平均每生只小鼠。在同样条件下进行许多,Aa2×Aa2的杂交,后代中AA占1/4,由于AA纯合胚胎致死,预期每窝平均生8×(3/4)=6只小鼠。(4)检测黄色雄鼠的基因型,应选择测交方法。实验思路和结果预测见答案所示。

以上就是2022英语周报七年级新目标YYY答案，更多英语周报答案请关注本网站。