单选题一个女人的父亲是色盲，她的兄弟中有两人和一个舅舅是血友病患者如果这个女人有一个血友病的患儿，则她的基因型必定是什么?( )

单选题在减数分裂的前期Ⅰ，看到有由一对同源染色体共同形成的圈的个体应为______。 A．缺失杂合体 B．重复杂合体 C．倒位杂合体 D．易位杂合体

单选题E. coli DNA polymerase Ⅰ具有3′→5′和5′→3′外切核酸酶活性，这两种酶活性的区别在于 a．3′→5′活性只切割碱基配对处的二酯键；b．5′→3′活性只切割碱基不配对处的二酯键； c．3′→5′活性只切割碱基不配对处的二酯键； d．两种活性对切割处的碱基配对与否无选择，只是5′→3′活性一次只切除一个核苷酸。

单选题果蝇中某一X连锁基因杂合时，表现缺刻翅，纯合致死，雌性缺刻翅个体与正常翅雄性个体进行杂交，下列哪种组合子代表现型是正确的______

单选题老鼠中，毛色基因位于常染色体上，黑毛对白毛为完全显性，如果白毛与黑毛杂合体杂交，子代将显示______。 A.黑毛:白毛=1:1 B.黑毛:白毛=3:1 C.全部黑色 D.不能确定

单选题毕业后，你和19个朋友制作了一个木筏，来到一个荒岛上开始建立新的种群，荒岛完全与世隔绝。两个朋友带有囊肿性纤维化的隐性致病基因。在荒岛上囊肿性纤维化的发病率是( )。

单选题Scholars of human migration speak of two main factors that influence an individual's decision to move from one place to another-push and pull factors. Push factors are associated with the place of origin. A push factor can be as simple and mild a matter as difficulty in finding a suitable job, or as traumatic as religious persecution, war, or severe famine Obviously, refugees who leave their homes with guns pointed at their heads or with hate-filled mobs at their heels are motivated almost entirely by push factors (although pull factors do influence their choice of destination). Pull factors are those associated with the place of destination. Most of these are economic, such as better job opportunities or the availability of good land to farm. The latter was an important factor in attracting settlers to the United States during the nineteenth century. In general, pull factors add up to an apparently better chance for a good life and material well-being than is offered by the place of origin. Besides push and pull factors, there are what the sociologists call " intervening obstacles " . Even if push and/or pull factors are very strong, they still may be outweighed by intervening obstacles, such as the distance of the move, the trouble and cost of moving, the difficulty of entering the new country, and the problems likely to be encountered on arrival. The decision to move is also influenced by " personal factors " of the potential migrant. The same push-pull factors and obstacles operate differently on different people, sometimes because they are at different stages of their lives, or just because of their varied abilities and personalities. The prospect of pulling up stakes and moving to a new and perhaps very strange environment may appear interesting and challenging to a young, footloose man and appallingly difficult to a slightly older man with a wife and young children. Similarly, the need to learn a new language and customs may intrigue one person and frighten another. Regardless of why people move, migration of large numbers of people causes friction. The United States and other " receiving countries " (the term used for countries that welcome large numbers of migrants) have experienced adjustment problems with each new wave of immigrants. The newest arrivals are usually given the lowest-paying jobs and are resented by natives who may have to compete with them for those jobs. It has usually taken several decades for each group to gain acceptance in the mainstream of society in the receiving country.

单选题作物品种甲比品种乙产量高15%，品种乙的含油量比品种甲的含油量高10%。产量和含油量这两个性状各由10对基因位点控制，彼此之间没有显隐性关系。为了选育产量高、品质好的新品种，将甲乙两品种杂交，试问，在F2中兼有双亲优点的个体比例有多少?( )

单选题Most worthwhile careers require some kind of specialized training. Ideally, therefore, the choice of an (1) should be made even before the choice of a curriculum in high school. Actually, (2) , most people make several job choices during their working lives, (3) because of economic and industrial changes and partly to improve (4) position. The "one perfect job" does not exist. Young people should (5) enter into a broad flexible training program that will (6) them for a field of work rather than for a single (7) . Unfortunately many young people have to make career plans (8) benefit of help from a competent vocational counselor or psychologist. Knowing (9) about the occupational world, or themselves for that matter, they choose their lifework on a hit-or-miss (10) .Some drift from job to job. Others (11) to work in which they are unhappy and for which they are not fitted. One common mistake is choosing an occupation for (12) real or imagined prestige. Too many high school students-or their parents for them-choose the professional field, (13) both the relatively small proportion of workers in the professions and the extremely high educational and personal (14) . The imagined or real prestige of a profession or a "white collar" job is (15) good reason for choosing it as life's work. (16) , these occupations are not always well paid. Since a large proportion of jobs are in mechanical and manual work, the (17) of young people should give serious (18) to these fields. Before making an occupational choice, a person should have a general idea of what he wants (19) life and how hard he is willing to work to get it. Some people desire social prestige, others intellectual satisfaction. Some want security, others are willing to take (20) for financial gain. Each occupational choice has its demands as well as its rewards.

单选题锥实螺Dd×Dd，后代为 ____ 。

单选题The food you eat does more than provide energy. It can have a dramatic effect on your body's ability to fight off heart disease, cancer, diabetes, high blood pressure, stroke, and weak bones. With remarkable consistency, recent research has found that a diet high in plant-based foods—fruits, vegetables, dried peas and beans, grains, and starchy staples such as potatoes—is the body's best weapon in thwarting many health-related problems. These foods work against so many diseases that the same healthy ingredients you might use to protect your heart or ward off cancer will also benefit your intestinal tract and bones. Scientists have recently estimated that approximately 30 to 40 percent of all cancers could be averted if people ate more fruits, vegetables, and plant-based foods and minimized high-fat, high-calorie edibles that have scant nutritional value. Up to 70 percent' of cancers might be eliminated if people also stopped smoking, exercised regularly, and controlled their weight. In the past, researchers had linked fat consumption with the development of cancers, but they currently believe that eating fruits, vegetables, and grains may be more important in preventing the disease than not eating fat. "The evidence about a high-fat diet and cancer seemed a lot stronger several years ago than it does now," says Melanie Polk, a registered dietitian and director of nutrition education at the American Institute for Cancer Research. The road to strong bones is paved with calcium-rich food. Leafy green vegetables and low-fat dairy products are excellent sources of calcium, the mineral that puts stiffness into your skeletal system and keeps your bones from turning rubbery and fragile. Your body uses calcium for more than keeping your bones strong. Calcium permits cells, to divide, regulates muscle contraction and relaxation, and plays an important role in the movement of protein and nutrients inside cells. If you don’t absorb enough from what you eat to satisfy these requirements, your body will take it from your bones. Because your body doesn't produce this essential mineral, you must continually replenish the supply. Even though the recommended daily amount is 1,200mg, most adults don't eat more than 500mg. One reason may have been the perception that calcium-rich dairy products were also loaded with calories. "In the past, women, in particular, worried that dairy products were high in calories," says Letha Y. Griffin, M. D. , of Peachtree Orthopaedics in Atlanta. "But today you can get calcium without eating any high-fat or high-calorie foods by choosing skim milk or low-fat yogurt." Also, low-fat dairy products contain phosphorous and magnesium and are generally fortified with vitamin D, all of which help your body absorb and use calcium. If you find it difficult to include enough calcium in your diet, ask your doctor about supplements. They're a potent way to get calcium as well as vitamin D and other minerals. But if you rely on pills instead of a calcium-rich diet, you won't benefit from the other nutrients that food provides. Getting the recommended vitamin D may be easy, since your body makes the vitamin when your skin is exposed to the sun's rays.

单选题1个在ABO基因位点的等位基因用IA，IB和i表示，1个B型血的个体的基因型则为IBIB或IBi。该等位基因在人群中的频率用p(IA)、q(IB)和r(i)表示。假设个体的交配相对于ABO位点来说是随机的。

单选题叶绿体有内外两层膜，其所需的蛋白质与膜相连并通过膜而进入的机制是 a．前体蛋白质(precursor)直接与膜相连； b．蛋白质N端加一前导序列； c．蛋白质C端加一后置序列； d．蛋白质内部加一信号序列。

单选题正常豚鼠具有黑褐色毛，可是偶尔的兄妹间交配却发现了两个突变体，它们都是淡黄色毛。下图是突变发生的家谱图，最初的亲本用X、Y表示。在实验室中，它们相互交配，所有的子代都正常。从图资料看，这种淡黄色毛的遗传可解释为______

单选题生物进化的实质是( )。

单选题今有一个植物雄性不育系，经检查，其雄花有花粉但败育，令其与恢复系杂交，结果杂种植株全部散粉且花粉全可育，又经与其不育系回交，回交群体呈现1:3的育与不育株的分离。则不育系与几对核基因有关______。 A．1对 B．2对 C．3对 D．4对

单选题一个AB血型的男人与一个B血型的女人结婚，生了4个孩子，第一个是AB型，第二个是O型，第三个是B型，第四个是A型，后来，由于夫妻不和，丈夫提出离婚，声称经血型家系分析，他不可能是所有孩子的父亲，他说的有道理么?______ A．对，因为O型不是他的孩子 B．对，因为B型不是他的孩子 C．对，因为AB型不是他的孩子 D．对，因为一个以上的孩子不是他的孩子 E．不对，因为所有的孩子都是他的孩子

单选题某二倍体生物的某一性状由4个复等位基因A，、A，、九和A：所控制，则群体中可 能出现的基因型种类有

单选题性连锁基因的剂量补偿效应：______。 A．在人类，通过Lyon化机制实现，正常女性个体细胞中的两条X染色体必有一条随即失活 B．在果蝇，通过特殊的Lyon化机制实现：正常雄性个体细胞中的X染色体基因超表达 C．在人类，通过女性细胞中一条X染色体失活实现；在果蝇，通过X染色体数目变化实现 D．上述选项中A和B正确