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  • General

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  • 遗传疾病

    What you will learn
    ::你会学到什么

    • Common genetic disorders in humans and how they are caused
      ::人类常见遗传疾病及其原因
    • Chromosomal disorders and their modes of inheritance
      ::染色体紊乱及其继承方式
    • How genetic disorders are diagnosed and treated
      ::如何诊断和治疗遗传病

    A small horse with a thick mane stands in a grassy field.

    Is being short-statured inherited?
    ::短暂的继承吗?

    It can be. Achondroplasia is the most common form of dwarfism in humans, which can also be observed in other such as horses. In humans, it is caused by a dominant . The mutation can be passed from one generation to the next.
    ::可能是的。 亚琴乌狄拉西亚是人类中最常见的侏儒主义形式, 也可以在马匹等其他生物中观察到。 在人类中,它是由支配力造成的。 突变可以代代相传。

    Genetic Disorders
    ::遗传疾病

    Many genetic disorders are caused by mutations in one or a few genes . Other genetic disorders are caused by abnormal numbers of .
    ::许多遗传障碍是由一种或几种基因的突变引起的,其他遗传障碍是由异常数目引起的。

    Genetic Disorders Caused by Mutations
    ::变异引起的遗传疾病

    The Table lists several genetic disorders caused by mutations in just one gene. Some of the disorders are caused by mutations in autosomal genes, others by mutations in X-linked genes . Which disorder would you expect to be more common in males than females? 
    ::表格列出了只由一个基因突变引起的几种遗传性疾病,有些是由自主基因突变引起的,有些则是由X相关基因突变引起的。 你期望男性中哪一种疾病比女性更常见?

    Genetic Disorder Direct Effect of Mutation Signs and Symptoms of the Disorder Mode of Inheritance
    Marfan syndrome defective in connective tissue heart and defects and unusually long, slender limbs and fingers autosomal dominant
    Sickle anemia abnormal hemoglobin protein in red blood cells sickle-shaped red blood cells that clog tiny , causing pain and damaging organs and autosomal recessive
    Vitamin D-resistant rickets lack of a substance needed for bones to absorb minerals soft bones that easily become deformed, leading to bowed legs and other skeletal deformities X-linked dominant
    Hemophilia A reduced activity of a protein needed for clotting internal and external bleeding that occurs easily and is difficult to control X-linked recessive

    Few genetic disorders are controlled by dominant alleles . A mutant dominant allele is expressed in every individual who inherits even one copy of it. If it causes a serious disorder, affected people may die young and fail to reproduce. Therefore, the mutant dominant allele is likely to die out of the .
    ::很少有遗传病是由占支配地位的异种控制。 遗传异种占支配地位的异种在每一个继承者身上都表现为占支配地位的异种。 如果它造成严重的紊乱,受影响的人可能会早死而不会繁殖。 因此, 变种主要异种很可能从中死亡 。

    A mutant recessive allele , such as the that causes sickle cell anemia (see the  Figure ), is not expressed in people who inherit just one copy of it. These people are called carriers . They do not have the disorder themselves, but they carry the mutant allele and can pass it to their offspring. Thus, the allele is likely to pass on to the next generation rather than die out. 
    ::基因变异的休眠配方,比如导致镰状细胞贫血(见图 ) , 并不表现在只继承一份细胞贫血的人身上。 这些人被称为携带者。 他们本身没有病症, 但是他们携带变异的止痛配方, 可以传给后代。 因此, 基因变异会传给下一代, 而不是死亡 。

    Comparison of normal and sickle-shaped red blood cells affected by sickle cell anemia.
    Sickle-Shaped and Normal Red Blood Cells. Sickle cell anemia is an autosomal recessive disorder. The mutation that causes the disorder affects just one amino acid in a single protein, but it has serious consequences for the affected person. This photo shows the sickle shape of red blood cells in people with sickle cell anemia.

    Chromosomal Disorders
    ::染色体紊乱

    Mistakes may occur during that result in nondisjunction . This is the failure of replicated chromosomes to separate during meiosis. Some of the resulting gametes will be missing a chromosome, while others will have an extra copy of the chromosome. If such gametes are fertilized and form zygotes , they usually do not survive. If they do survive, the individuals are likely to have serious genetic disorders. The Table lists several genetic disorders that are caused by abnormal numbers of chromosomes. Most chromosomal disorders involve the X chromosome . Look back at the X and Y chromosomes and you will see why. The X and Y chromosomes are very different in size, so nondisjunction of the sex chromosomes occurs relatively often. 
    ::在这种结果中,可能会发生错误,结果不相容。这就是复制的染色体在 meiscois 期间无法分离。 由此产生的部分配色体会缺少染色体, 而另一些则会增加染色体的复制件。 如果这些配色体被施肥并形成酶, 它们通常不会存活下来。 如果它们生存下来, 个人可能会有严重的遗传障碍。 表格列出了一些由染色体异常数造成的遗传障碍。 大多数染色体紊乱都涉及X染色体。 回顾X和Y染色体,你会看到原因。 X和Y染色体的大小差异很大, 因而性染色体的不相交性会比较频繁。

    Genetic Disorder Genotype Phenotypic Effects
    Down syndrome extra copy (complete or partial) of chromosome 21 (see the Figure ) developmental delays, distinctive facial appearance, and other abnormalities (see the Figure )
    Turner syndrome one X chromosome but no other sex chromosome (XO) female with short height and infertility (inability to reproduce)
    Triple X syndrome three X chromosomes (XXX) female with mild developmental delays and menstrual irregularities
    Klinefelter syndrome one Y chromosome and two or more X chromosomes (XXY, XXXY) male with problems in sexual and reduced levels of the testosterone
    • Chromosomal map showing typical and abnormal arrangements related to Klinefelter syndrome.
    • A baby’s face, representing characteristics associated with genetic disorders.
    (First) Trisomy 21 (Down Syndrome) Karyotype. A karyotype is a picture of a cell's chromosomes. Note the extra chromosome 21. (Second) Child with Down syndrome, exhibiting characteristic facial appearance.
    DID YOU KNOW?
    Over 6,000 genetic disorders are known, with new ones being added to the list constantly. These disorders are also quite common. For instance, single-gene disorders affect around one in 50 people!  
     

    Diagnosing Genetic Disorders
    ::诊断遗传疾病

    A genetic disorder that is caused by a mutation can be inherited. Therefore, people with a genetic disorder in their family may be concerned about having children with the disorder. Professionals known as genetic counselors can help them understand the risks of their children being affected. If they decide to have children, they may be advised to have prenatal (“before birth”) testing to see if the fetus has any genetic abnormalities. One method of prenatal testing is amniocentesis . In this procedure, a few fetal cells are extracted from the fluid surrounding the fetus, and the fetal chromosomes are examined.
    ::突变导致的遗传障碍可以继承。因此,家庭中的遗传障碍患者可能担心有孩子患有这种紊乱。被称为遗传顾问的专业人员可以帮助他们了解子女受到影响的风险。如果他们决定生孩子,可以建议他们进行产前(“出生前”)检查,看胎儿是否有任何遗传异常。产前检查的一种方法是羊膜检查。在这个过程中,从胎儿周围的液体中抽取了几个胎儿细胞,并对胎儿染色体进行检查。

    Treating Genetic Disorders
    ::治疗遗传病

    The symptoms of genetic disorders can sometimes be treated, but cures for genetic disorders are still in the early stages of development. One potential cure that has already been used with some success is . This involves inserting normal genes into cells with mutant genes.
    ::基因紊乱症状有时可以治疗,但基因紊乱的治疗仍处于早期发育阶段,一种已经成功使用的潜在治疗方法就是:将正常基因与变种基因植入细胞。

    If you could learn your risk of getting or another genetic disease, would you? Though this is a personal decision, it is a possibility. A number of companies now make it easy to order medical genetic tests through the Web. 
    ::如果你能知道自己有染上遗传病或其他遗传疾病的风险,你会吗?虽然这是个人的决定,但有可能。一些公司现在很容易通过网络进行医学基因测试。

    Check your understanding!
    ::检查你的理解!

     

     

     

     

     

    Summary
    ::摘要

    • Many genetic disorders are caused by mutations in one or a few genes.
      ::许多遗传疾病是由一种或几种基因的突变引起的。
    • Other genetic disorders are caused by abnormal numbers of chromosomes.
      ::其他遗传疾病是由异性染色体的异常数量引起的。

    Review
    ::回顾

    1. Describe a genetic disorder caused by a mutation in a single gene.
      ::描述单一基因突变引起的遗传障碍。
    2. What causes Down syndrome?
      ::什么原因导致唐氏综合症?
    3. What is nondisjunction?
      ::什么是互不相容?
    4. What is gene therapy?
      ::什么是基因疗法?
    5. Explain why genetic disorders caused by abnormal numbers of chromosomes most often involve the X chromosome.
      ::解释为什么由异常数量的染色体引起的遗传疾病最经常涉及X染色体。