转基因动物.doc

准备假孕母鼠
受精卵的准备
基因导入
胚胎移植
对幼鼠鉴定
外源DNA大小基本不受控制(1-50kb)
导入过程直观
整合效率高
设备昂贵,环节较多
对操作人员有较高的技术要求
低效率(尤其是对大家畜)
对卵子伤害大,胚胎存活率低
基因整合随机性
转基因沉默
基因导入的方法
受精卵雄原核显微注射法
胚胎干细胞法
逆转率病毒感染法
A new study has found the amount of antibiotics given to farm animals is expected to increase by two-thirds over the next 15 years. Researchers are linking the growing dependence on the drugs to rising demand for meat, milk and eggs. The researchers warn the drugs could quicken the development of antibiotics-resistant infections. Such infections are already a major public health concern in the United States.
Experts say when people stop living in poverty, the first thing they want to do is eat better. For most people, that means eating more meat.
Increasing prosperity in Asia has meant people there are eating nearly four times as much meat, milk and dairy products as they did 50 years ago.
To meet that demand, farms have put many animals into smaller spaces.
Gail Hansen is a veterinarian -- a doctor who treats animals -- with the Pew Charitable Trusts, a research and advocacy group.
"As the animals are crowded together, oftentimes the easiest way to deal with some of the problems of crowding is to give them antibiotics."
Dr. Hansen says antibiotics help the animals stay healthy in crowded environments and grow faster. But bacteria can develop resistance to the drugs, and that now-resistant b