上海留学中介

Mutations are errors in the genotype that create new alleles and can result in a

variety of genetic disorders. In order for a mutation to be inherited from one

generation to another, it must occur in x cells, such as eggs and sperm, rather

than in somatic cells. The best way to detect whether a genetic disorder exists is

to u a karyotype, a photograph of the chromosomes from an individual cell,

usually lined up in homologous pairs, according to size.

Autosomal Mutations

Some human genetic illness are inherited in a Mendelian fashion. The dia

phenotype will have either a clearly dominant or clearly recessive pattern of

inheritance, similar to the traits in Mendel’s peas. Such a pattern will usually only

occur if the dia is caud by an abnormality in a single gene. The mutations

that cau the dias occur in genes on the autosomal chromosomes, as

oppod to x-­‐linked dias, which we cover later in this chapter. (Be careful

not to confu autosomal chromosomes with somatic cells; autosomal

chromosomes are the chromosomes that determine bodily characteristics and

exist in all cells, both x and somatic.)

Recessive Disorders

A Mendelian genetic illness initially aris as a new mutation that changes a

single gene so that it no longer produces a protein that functions normally. Some

mutations, however, result in an allele that produces a nonfunctional protein. A

dia resulting from this sort of mutation will be inherited in a recessive

fashion: the dia phenotype will only appear when both copies of the gene

carry the mutation, resulting in a total abnce of the necessary protein. If only

one copy of the mutated allele is prent, the individual is a heterozygous carrier,

showing no signs of the dia but able to transmit the dia gene to the next

generation. Albinism is an example of a recessive illness, resulting from a

mutation in a gene that normally encodes a protein needed for pigment

production in the skin and eyes. The pedigree shown below diagrams three

generations of a hypothetical family affected by albinism.

是美国某知名教育集团做的上海教育市场调查的部分内容，为内部资料。是在该

集团实习的员工发到网上的。不同于北京和广东媒体按赞助费广告费给的评比标

准，是最全面最真实的上海美国留学中介排名。对学生找上海美国留学中介很有

帮助。

知名度排名：（满分5分）

1. 中智留学（5）

2. 美勤留学（4.1）

3. 中锐留学（3.2）

4. 上教留学（3.1）

5. 东方留学（3.0）

专业度排名：（满分5分）

1. 美勤留学（4.9）

2. 伯乐留学（4.4）

3. 中智留学（4）

4. 华侨留学（3.4）

5. 学美留学（3.3）

录取满意度排名（满分5分）

1. 美勤留学（4.2）

2. 上教留学（4）

3. 太傻留学（3.9）

4. 学美留学（3.2）

5. 中智留学（3）

评选原则：

美国留学中介质量排名：这些最近更新的美国留学中介排名的重点在三个因素，

一个良好的知名度的评分、一个被认可的咨询顾问的专业度的评分、委托办理美

国留学的学生对录取满意度的评分。这与家长与学生的立场一致。