题目

Now many young people are traveling around the world on their own，not because they have no one to travel with，but because they prefer to go alone. Kristina Wegscheider from California first traveled alone when she was at college and believes that it is something everyone should do at least once in their life. ＂It opens up your mind to new things and pushes you out of your comfort zone.＂ Wegscheider has visited 46 countries covering all seven continents. In foreign countries，with no one to help you read a map，look after you if you get ill，or lend you money if your wallet i某研究小组利用玉米种子作为实验材料，进行育种实验。（1）培育四倍体玉米，可用秋水仙素诱导玉米萌发的种子；秋水仙素作用于细胞分裂 期，为鉴定形成的植株是否为多倍体，取玉米根尖→解离→漂洗→用 染色→制片→用显微镜观察细胞中染色体数目。（2）有甲、乙、丙、丁四个品系的纯种玉米，基因型分别为AABBGG、aaBBGG、 AAbbGG、AABBgg。若想培育出AaaBBbGGG新类型，试用遗传图解表示育种的过程。（3）单倍体育种可以缩短育种年限。现有基因型为DdTt的玉米种子，利用其快速培育基因型为ddTT的玉米植株的过程是：种植玉米种子，长成植株后，进行 获得单倍体幼苗，再用 处理。为判断玉米单倍体植株是否加倍成功，可以观察植株是否散粉和 来判断。(4)如果某玉米种群不具有抗虫基因，则一般通过 育种获得具有抗虫性状的玉米新品种；如果某玉米种群的玉米产量一直比较低，则可利用该种群获得的玉米种子进行育种获得产量比较高的玉米新品种，这种育种方法的原理是 。