Section outline

  • General

    Collapse all Expand all

  • 案例研究:基因和继承

    lesson content

    Case Study: Cancer in the Family
    ::案例研究:家庭癌症

    People tend to look similar to their biological parents, as illustrated by the family tree above. Beyond just appearance , you can also inherit traits from your parents that you can’t see.
    ::人们看起来往往和亲生父母相似,上面的家族树就说明了这一点。 除了外表外,你还可以继承你无法看得见的父母的特质。

    Rebecca becomes very aware of this fact when she visits her new doctor for a physical exam. Her doctor asks several questions about her family medical history, including whether Rebecca has or had relatives with cancer. Rebecca tells her that her grandmother, aunt, and uncle — who have all passed away — had cancer. They all had breast cancer, including her uncle, and her aunt also  had ovarian cancer. Her doctor asks how old they were when they were diagnosed with cancer. Rebecca is not sure exactly, but she knows that her grandmother was fairly young at the time, probably in her forties.
    ::Rebecca在去看她的新医生进行身体检查时非常了解这一事实。她的医生问了一些关于她家庭医疗史的问题,包括Rebecca是否患有癌症。Rebecca告诉她,她祖母、姑姑和叔叔——他们都已经去世了——都得了癌症。他们都患有乳腺癌,包括她的叔叔,她的姨妈也患有卵巢癌。她的医生问她们被诊断患有癌症时的年纪有多大。Rebecca并不确切地确定,但她知道她祖母当时相当年轻,大概在她的四十多岁。

    Rebecca’s doctor explains that while the vast majority of cancers are not due to inherited factors, a cluster of cancers within a family may indicate that there are mutations in certain genes that increase the risk of getting certain types of cancer, particularly breast and ovarian cancer. Some signs that cancers may be due to these genetic factors are present in Rebecca’s family, such as cancer with an early age of onset (e.g. breast cancer before age 50), breast cancer in men, and breast cancer and ovarian cancer within the same person or family.
    ::Rebecca的医生解释说,尽管绝大多数癌症不是遗传因素造成的,但家庭内部的一系列癌症可能表明某些基因的突变增加了患某些类型癌症的风险,特别是乳腺癌和卵巢癌。 某些迹象显示,这些遗传因素可能导致癌症在Rebecca的家庭中出现,比如早发癌症(如50岁前的乳腺癌 ) 、 男性乳腺癌、同一个人或同一家庭中的乳腺癌和卵巢癌。

    Based on her family medical history, Rebecca’s doctor recommends that she see a genetic counselor, because these professionals can help determine whether the high incidence of cancers in her family could be due to inherited mutations in their genes. If so, they can test Rebecca to find out whether she has the particular variations of these genes that would increase her risk of getting cancer.
    ::根据家庭病史,Rebecca的医生建议她找一位遗传顾问,因为这些专业人士可以帮助确定家庭癌症发病率高是否是由于遗传基因的突变所致。 如果是这样,他们可以测试Rebecca,看看她是否拥有这些基因的特殊变异性,从而增加她患癌症的风险。

    When Rebecca sees the genetic counselor, he asks how her grandmother, aunt, and uncle with cancer are related to her. She says that these relatives are all on her mother’s side — they are her mother’s mother and siblings. The genetic counselor records this information in the form of a specific type of family tree, called a pedigree, indicating which relatives had which type of cancer, and how they are related to each other and to Rebecca.
    ::当Rebecca看到遗传顾问时,他问她祖母、姑姑和患癌症的叔叔与她有何关系。 她说这些亲戚都站在她母亲一边 — — 他们是她母亲的母亲和兄弟姐妹。 遗传顾问以特定类型的家族树形式记录了这一信息,叫做小树,表明哪位亲属患了哪种癌症,以及他们彼此之间和Rebecca之间有何关系。

    He also asks her ethnicity. Rebecca says that her family on both sides are Ashkenazi Jews (Jews whose ancestors came from central and eastern Europe). “But what does that have to do with anything?” she asks. The counselor tells Rebecca that mutations in two tumor-suppressor genes called BRCA1 and BRCA2, located on chromosome 17 and 13, respectively, are particularly prevalent in people of Ashkenazi Jewish descent and greatly increase the risk of getting cancer. About one in 40 Ashkenazi Jewish people have one of these mutations, compared to about one in 800 in the general population. Her ethnicity, along with the types of cancer, age of onset, and the specific relationships between her family members who had cancer, indicate to the counselor that she is a good candidate for genetic testing for the presence of these mutations.
    ::他还询问她的族裔。Rebecca说,她的双方家庭都是Ashkenazi犹太人(其祖先来自中欧和东欧的犹太人) 。 “ 但是这又有什么关系?” 她问。 顾问告诉Rebecca说,两种肿瘤抑制基因的突变分别发生在17和13个染色体上的BRCA1和BRCA2, 在Ashkenazi犹太血统的人中特别普遍,并大大增加了患癌症的风险。 大约40个Ashkenazi犹太人中有一个有这种突变,而一般人口中只有800个。 她的种族,以及癌症、发病年龄和患癌症的家庭成员之间的具体关系,都向顾问指出,她是这些突变的遗传测试的好人选。

    Rebecca says that her 72-year-old mother never had cancer, and nor had many other relatives on that side of the family. How could the cancers be genetic? The genetic counselor explains that the mutations in the BRCA1 and BRCA2 genes, while  dominant, are not inherited by everyone in a family. Also, even people with mutations in these genes do not necessarily get cancer — the mutations simply increase their risk of getting cancer. For instance, 55 to 65 percent of women with a harmful mutation in the BRCA1 gene will get breast cancer before age 70, compared to 12 percent of women in the general population who will get breast cancer sometime over the course of their lives.
    ::Rebecca说,她72岁的母亲从未患过癌症,而且家里还有许多其他亲属。这些癌症怎么会是遗传的?遗传顾问解释说,BRCA1和BRCA2基因的突变虽然占主导地位,但并非由家庭中的每一个人继承。 此外,即使这些基因的突变者也不一定得癌症 — — 这些突变只是增加了她们患癌症的风险。 比如,在BRCA1基因中发生有害突变的妇女中,55%至65%将在70岁前得乳腺癌,而在普通人口中,有12%的妇女将在一生中得乳腺癌。

    Rebecca is not sure she wants to know whether she has a higher risk of cancer. The genetic counselor understands her apprehension, but explains that if she knows that she has harmful mutations in either of these genes, her doctor will screen her for cancer more often and at earlier ages. Therefore, any cancers she may develop are likely to be caught earlier when they are often much more treatable. Rebecca decides to go through with the testing, which involves taking a blood sample, and nervously waits for her results.
    ::Rebecca并不确定她是否想知道自己是否有更高的癌症风险。 遗传顾问理解她的担忧,但解释说,如果她知道自己在这两种基因中都有有害的突变,她的医生会更经常和更早地检查她的癌症。 因此,她可能患上的任何癌症都有可能早些感染,而当这些癌症通常更容易治疗时。 Rebecca决定进行测试,包括验血样本,并紧张地等待结果。

    Chapter Overview: Genetics
    ::第一章 概述:遗传学

    At the end of this chapter, you will find out Rebecca’s test results. By then, you will have learned how traits are inherited from parents to offspring through genes, and how mutations in genes such as BRCA1 and BRCA2 can be passed down and cause disease. Specifically, you will learn about:
    ::本章结尾处,你将会发现Rebecca的测试结果。 到那时,你将了解如何通过基因从父母遗传给后代,以及BRCA1和BRCA2等基因的突变如何被传染并导致疾病。 具体而言,你将了解:

    • How genes and their different alleles are located on chromosomes
      ::如何将基因和不同基因的异系细胞 定位在染色体上
    • The 23 pairs of human chromosomes, which include autosomes and sex chromosomes
      ::23对人类染色体,包括异体和性染色体
    • How DNA was found  to be the inherited genetic material
      ::如何发现DNA是遗传遗传物质
    • The structure of DNA
      ::DNA结构结构
    • How DNA replication occurs
      ::如何复制DNA
    • The central dogma of molecular biology, which describes how DNA is transcribed into RNA, and then translated into proteins
      ::分子生物学的核心教条,它描述了DNA如何被转录到RNA,然后转化成蛋白质
    • The structure, functions, and possible evolutionary history of RNA
      ::RNA的结构、功能和可能的演变历史
    • How genes code for proteins using codons made of the sequence of nitrogen bases within RNA and DNA
      ::如何使用由RNA和DNA内氮基序列组成的coddon 生成的蛋白质基因编码
    • How proteins are synthesized through the transcription of RNA from DNA and the translation of protein from RNA, including how RNA and proteins can be modified, and the roles of the different types of RNA
      ::如何通过从DNA转录RNA并翻译RNA的RNA来合成蛋白质,包括如何改变RNA和蛋白质,以及不同类型RNA的作用
    • What mutations are, what causes them, different specific types of mutations, and the importance of mutations in evolution and to human health
      ::变异是什么,导致变异的原因是什么,变异的不同具体类型,变异在进化和人类健康中的重要性
    • How the expression of genes into proteins is regulated and why problems in this process can cause diseases, such as cancer
      ::如何规范基因表现成蛋白质的表达方式,以及为什么这一进程中的问题可能造成癌症等疾病。
    • How Gregor Mendel discovered the laws of inheritance for certain types of traits
      ::Gregor Mendel是如何发现某些特性的继承法的
    • The science of heredity, known as genetics, and the relationship between genes and traits
      ::遗传科学,称为遗传学,以及基因和特性之间的关系
    • How gametes, such as eggs and sperm, are produced through meiosis
      ::卵和精子等调子是如何通过线性硬化生成的
    • How sexual reproduction works on the cellular level and how it increases genetic variation
      ::性生殖如何在细胞层面运作,如何增加遗传变异
    • Simple Mendelian and more complex non-Mendelian inheritance of some human traits
      ::简单门德利文和更复杂的非门德利文人继承一些人类特质
    • Human genetic disorders, such as Down syndrome, hemophilia A, and disorders involving sex chromosomes
      ::人类遗传疾病,如唐氏综合症、血友病A和涉及性染色体的疾病
    • How biotechnology — which is the use of technology to alter the genetic makeup of organisms — is used in medicine and agriculture, how it works, and some of the ethical issues it may raise
      ::生物技术——即利用技术改变生物基因构成的技术——如何用于医药和农业,如何运作,以及它可能引起的一些伦理问题
    • The human genome, how it was sequenced, and how it is contributing to discoveries in science and medicine
      ::人类基因组,它是如何测序的, 它是如何促成科学和医学的发现的

    As you read this chapter, keep Rebecca’s situation in mind and think about the following questions:
    ::记住Rebecca的处境, 思考以下问题:

    1. What do the BRCA1 and BRCA2 genes normally do? How can they cause cancer?
    ::1. BRCA1和BRCA2基因通常做什么?如何导致癌症?

    2. Are BRCA1 and BRCA2 linked genes? Are they on autosomes or sex chromosomes?
    ::2. BRCA1和BRCA2是连接基因的吗?它们是在异体基因还是性染色体基因?

    3. After learning more about pedigrees, draw the pedigree for cancer in Rebecca’s family. Use the pedigree to help you think about why it is possible that her mother does not have one of the BRCA gene mutations, even if her grandmother, aunt, and uncle did have it.
    ::3. 在更多了解小儿麻痹后,在Rebecca家里绘制癌症小儿麻痹图,用小儿麻痹图帮助你考虑为什么她母亲没有BRCA基因突变,即使她祖母、姑姑和叔叔确实有。

    4. Why do you think certain gene mutations are prevalent in certain ethnic groups?
    ::4. 为什么你认为某些基因突变在某些族裔群体中很普遍?