听力原文:W: Can you figure out what's wrong with John? He doesn't talk to anyone since last week? M: He's had a terrible time with his wife. But it has something to do with his parents. Q: What conclusion can you draw from the conversation? (19)
A.
He has some trouble with his parents.
B.
His parents had a quarrel.
C.
He and his wife might have had a quarrel.
D.
His wife and his parents might have disagreed with each other.
【单选题】研究表明,位于一对同源染色体上且相距非常远的两对非等位基因在染色体发生交叉互换后产生的配子种类和比例,与两对非等位基因自由组合产生的配子种类和比例难以区分。雌果蝇的细胞在减数分裂过程中染色体发生交叉互换,雄果蝇不发生。基因 M /m 和 N/ n 控制不同的相对性状,下列能证明果蝇的基因 M 和 N 位于同一染色体上且相距非常远的杂交组合是 ( )