问题 问答题

概述Mendel G.J.和Morgan T.H.对遗传学的主要贡献及他们学说的联系。

答案

参考答案:孟德尔从1856年起就在修道院的花园里种植豌豆,开始他的“豌豆杂交试验”,到1864年共进行了8年试验,发现了前人未认识到的规律,后来称为孟德尔定律,即分离定律(law of segregation)和自由组合定律(law of independent assortment),成为遗传学的奠基人,被誉为现代遗传学之父。美国的遗传学家摩尔根及他的学生们用果蝇做实验,创立了连锁交换律(law of linkage and crOssover)。
两学说共同指出了生物在形成配子时基因的传递规律。分离律指明了配子形成时,成对的等位基因彼此分开,分别进入不同的生殖细胞中去;自由组合律认为不成对的(非同源染色体上)等位基因在形成配子时自由组合;而连锁律表明了配子形成时基因的传递是以染色体为单位的,位于一条染色体上的基因是连锁在一起进行传递的;交换律说明了连锁不是绝对的,同源染色体上的基因可以发生交换。两学说并无矛盾,是生物配子发生时共同遵循的规律。

单项选择题
单项选择题

Questions 11~15
It’s estimated that every year 100,000 children aged 16 and under run away from home. The London Refuge, an unremarkable house on an unremarkable street, is the only place in Britain that will give them a bed. Last year it gave sanctuary to 238 children of whom the youngest was 11. What happened to the other 99,762 Nobody knows, although it’s a fair bet that some of them ended up on the streets, that some fell into inappropriate and dangerous company, that some didn’t survive. "The mere fact that they’re running away puts them at risk," says Lorna Simpson, the refuge’s deputy manager. "On the streets they’ 11 mix with other young people. They’ re so naive; they don’t understand that people who are nice to them will want payback. Our job is to make them safe. "
Simpson, a former social worker, is a calm woman of great warmth. The refuge has six beds and has been open since 1993, often with the threat of closure hanging over it. The problem has nothing to do with the quality of its service and everything to do with funding. A week’s placement costs £2. 278 and three successive governments have argued that the annual running costs of £720. 000 should be locally funded. But because it is used by children from many parts of London, and beyond, local authorities are reluctant to contribute.
The Government has now agreed to work on a strategy to support runaway children in England and Wales, which is rich after its withdrawal of funding from the refuge in December. Since then the NSPCC, National Society for the Prevention of Cruelty to Children, which runs the refuge in conjunction with St Christopher’s Fellowship, has financed it through a donation from an individual, but that money will last only until late next year. "Without this facility there’s nothing; children who run away are on the street," says Nasima Patel, the assistant director of the NSPCC. "One of the strengths of the refuge is that children who have left home can ring up directly and will get a bed and supportive staff without having to go through a process of assessment".
The refuge accommodates six children plus staff. Many of the admissions are at night and children can stay up to 21 days in three months, although most stay for three to five days. They find it through social services, through ChildLine and through word of mouth.
"Children run away from everything you can think of," Simpson says. "Arguments with step-parents, sexual abuse, alcoholic parents, being left to bring up their younger siblings, neglected children who have been failed by social services, girls who have been trafficked. We get doctors’ and lawyers’ children who run away because they want more pocket money, or want to stay out later than their parents allow. They’ve been given everything, they get to 15 and no one thinks to pull the reins in. By that time it’s too late; they rebel. "
Most of the children are from families known to social services, and for them the refuge’s ordered regimen is a welcome contrast to the chaos they know. Staff listen without judging and without encouraging dependency, trying to establish why the children have run away. The aim is to get them home or into the care of social services and, after discharge from the refuge, a family support worker is available.

What is Lorne Simpson’s concern about runaway children ______

A. They don’t understand people who are nice to them.
B. They have no direct access to the London Refuge.
C. They will distance themselves from their parents.
D. They will keep company with undesirables.