题目

John, 11 years old, was in bed in hospital. Two days ago, while he was ____ in a baseball game, he fell and hit his head. The doctor believed that he might ____ get well.“He seems to have given up hope. So medicine alone won’t ____. Perhaps（也许）he needs something else,” said a doctor. “When I visit him, all he ever says is that he would like to meet Babe Ruth.”To meet Babe Ruth, of course, was not ____ . In America, Babe Ruth was as ____ a man as the president himself, and he was the most famous baseball player.The next day John’s father managed（设法）to tell Babe Ruth 12．燕麦颖色受两对基因控制．现用纯种黄颖与纯种黑颖杂交，F1全为黑颖，F1自交产生的F2中，黑颖：黄颖：白颖=12：3：1．已知黑颖（B）和黄颖（Y）为显性，只要B存在，植株就表现为黑颖．请分析回答：（1）F2的性状分离比说明B（b）与Y（y）存在于两对染色体上．符合孟德尔的自由组合定律．（2）F2中，黄颖的基因型有两种，黑颖中纯合体的比例是$\frac{1}{6}$．（3）现有一黑颖个体，不知其基因型，选择表现型为bbyy的个体与其交配，若后代全是黑颖，则其基因型是BBYY、BBYy、Bbyy；若后代表现型及其比例是黑颖：黄颖：白颖=2：1：1；则其基因型是BbYy．