2022英语周报七年级第十三期七年级新目标答案

第一节One possible version:Dear Tony,Many thanks for your concern! Though Gaokao has been postponed due to theoverwhelming COVID-19, it is approaching day by day.Currently, I'm under unbearable pressure with endless tests to sit. I sometimes suffertest anxiety, which does upset me a lot. But what can't beat me can only serve to make mestronger. I'm positive that with adequate preparations, I'm getting closer and closer to mydream-to be a doctor to relieve pains of patients, which will motivate me to study harder.Best wishesYours,Li Hua

5.B(根据题意分析可知:果蝇的灰身和黑身由常染色体上的等位基因(B-b)控制,等位基因(R-r)位于X染色体上,说明控制体色的两对等位基因分别位于两对同源染色体上,因此在遗传过程中遵循自由组合定律。纯合的黑身雌果蝇与纯合的灰身雄果蝇杂交,F1全为灰身,子二代中雌、雄果蝇灰身:黑身〓3:1,其中雌果蝇没有深黑身,雄果蝇黑身:深黑身=1:1,说明子一代雄果蝇的基因型是BbXY,雌果蝇的基因型是BbXX,基因R、r中使黑身果蝇的体色加深的是基因r。因此,亲本雄果蝇的基因型是BBⅹY,雌果蝇的基因型是bbXX。现有的雌雄果蝇:亲本BBXY、 bbX R;子一代:BbXY、BbXX";子二代:BBXX、BBXX、BBXY、BBXY、 BbX XBbXX、BbXY、BbXY、bbXX、bbXX、bbXY、bbX"Y。其中能通过一次交配使雌雄子代同时具有三种表现型的杂交组合有以下三种:bbXX与BbXY;bbXY与BbXX;BbXY和BbX“X。故B正确,A、C、D错误。)

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