题干

科学家对白虎与黄虎的相关基因组分析,发现白虎毛色的形成,是由于某转运蛋白质第477位氨基酸位置上丙氨酸转变成了缬氨酸,导致色素水平下降,白虎的生理健康状况与黄虎没有差异.下列相关叙述正确的是(  )

A:白虎是由基因突变引起的白化病个体

B:决定白虎毛色和人的白化病症状的突变基因控制的途径是不同的

C:白虎毛色的形成可能是DNA分子中碱基对的增添或缺失造成的

D:白虎的观赏价值和科研价值分别体现了生物的直接价值和间接价值

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答案(点此获取答案解析)

B

同类题2

根据短文理解,从A、B、C、D四个选项中选择最佳的一个答案填空。
    Sometimes, I want to know whether there is any love between my parents. Every day, they are 1 trying to make money. They don't act romantically(浪漫地)the way couples(夫妇)do in books 2 on TV. They never say “I love you" to each other. It's not their 3.
    One day, my mother was sewing(缝) a quilt. I sat down next to 4. “Mom, I have a question to ask you," I said after a while. “What?" she asked, still working. 
   “Is there love 5 you and Dad?” I asked her in a very low 6.
    She stopped her work and 7 her head. Then she bowed(低下)her head and went on sewing.
    I thought I had hurt her. At last I heard my mother say, “Susan, look at this thread(线)Sometimes it 8, but most of it disappears in the quilt. It makes the quilt 9. If life 10 a quilt, then love should be a thread. It can 11 be seen anywhere, but it's really there.”
    I listened carefully but I didn't understand her 12 the next spring. My father suddenly got sick. My mother had to stay with him in the 13 for a month.
    After they got back, she helped my father walk slowly down the road every day. My father had never been so weak.
  “Dad,  14 are you feeling now?" I asked him one day.
  “Susan, don't worry about me,” he said gently “I just like 15 with your mom.” Once I thought love meant flowers, gifts and sweet kisses. Now, I know that love is the thread that holds a family together.