Section outline

  • General

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  • 变异效应

    What you will learn
    ::你会学到什么

    • How do affect an organism
      ::如何影响有机体
    • Beneficial and harmful mutations
      ::有益和有害的突变

    A hairless mouse with visible skin and a wrinkled body on a textured surface.

    Is this mouse hairless?
    ::这只老鼠是无毛的吗?

    Yes. Why? The result of a mutation, a change in the sequence. The effects of mutations can vary widely, from being beneficial, to having no effect, to having lethal consequences, and every possibility in between.
    ::为什么?变异的结果,序列的变化。变异的效果可以大不相同,从有益到无效,从产生致命后果到产生致命后果,以及两者之间的各种可能性。

    Effects of Mutations
    ::变异的影响

    The majority of mutations have neither negative nor positive effects on the organism in which they occur. These mutations are called neutral mutations . Examples include silent point mutations . They are neutral because they do not change the amino acids in the they encode.
    ::大多数突变对发生突变的有机体没有消极或积极影响。 这些突变被称为中性突变。 例如静点突变。 它们中立, 因为它们不会改变编码中的氨基酸 。

    Many other mutations have no effect on the organism because they are repaired before occurs. have multiple repair mechanisms to fix mutations in DNA. One way DNA can be repaired is illustrated in the  Figure . If a cell’s DNA is permanently damaged and cannot be repaired, the cell is likely to be prevented from dividing.
    ::许多其他突变对生物体没有影响,因为它们是在发生之前修复的。 具有多种修复机制来修复DNA中的突变。 图中说明了可以修复DNA的一种方式。 如果细胞的DNA被永久损坏,无法修复,那么细胞就可能无法分裂。

    Flow chart illustrating DNA repair in E. coli, detailing roles of Uvr proteins and DNA polymerase.
    DNA Repair Pathway. This flow chart shows one way that damaged DNA is repaired in E. coli bacteria. The repair proteins (Uvr-A, Uvr-B and Uvr-C) cut out the damaged nucleotides. The enzyme DNA polymerase adds correct nucleotides in their place and DNA ligase seals the gap after the repair.

     

     

     

     

    Beneficial Mutations
    ::受益性变异

    Some mutations have a positive effect on the organism in which they occur. They are called beneficial mutations . They lead to new versions of proteins that help organisms adapt to changes in their environment. Beneficial mutations are essential for evolution to occur. They increase an organism’s chances of surviving or reproducing, so they are likely to become more common over time. There are several well-known examples of beneficial mutations. Here are just two:
    ::一些突变对发生突变的有机体产生了积极影响。 它们被称为有益的突变。 它们带来新的蛋白质, 帮助生物体适应环境的变化。 进化过程中,福利性突变至关重要。 它们增加了生物体存活或再生的机会, 从而可能随着时间的流逝而变得更为常见。 有几个已知的有利变异的例子。 这里只有两个:

    1. Mutations in many that allow them to survive in the presence of antibiotic drugs . The mutations lead to antibiotic-resistant strains of bacteria.
      ::许多变异使它们得以在抗生素药物存在的情况下生存。 突变导致了抗生素抗菌菌株。
    2. A unique mutation is found in people in a small town in Italy. The mutation protects them from developing atherosclerosis , which is the dangerous buildup of fatty materials in . The individual in which the mutation first appeared has even been identified.
      ::在意大利的一个小镇上,人们发现一种独特的突变。突变保护他们避免发展无花生硬化,这是一种危险的脂肪材料堆积。突变最初出现的人甚至被识别出来。

    Harmful Mutations
    ::有害变异

    Imagine making a random change in a complicated machine such as a car engine. The chance that the random change would improve the functioning of the car is very small. The change is far more likely to result in a car that does not run well or perhaps does not run at all. By the same token, any random change in a gene's DNA is likely to result in a protein that does not function normally or may not function at all. Such mutations are likely to be harmful. Harmful mutations may cause or .
    ::想象一下在汽车引擎等复杂机器中随机改变的可能性。 随机改变能改善汽车功能的可能性很小。 改变更有可能导致汽车运行不顺利或可能根本不运行。 同样, 基因DNA的任何随机改变都可能导致蛋白质不正常或根本不能发挥作用。 这种突变很可能有害。 有害的突变可能会造成或egg 。

    • A genetic disorder is a disease caused by a mutation in one or a few genes . A human example is cystic fibrosis . A mutation in a single gene causes the body to produce thick, sticky mucus that clogs the lungs and blocks ducts in digestive organs . 
      ::基因紊乱是一种或数种基因突变引起的疾病。 人类的一个例子是细胞纤维化。 单一基因的突变导致身体产生厚粘粘的粘性粘性粘性粘性粘性,将肺部和消化器官的管管堵塞。
    • Cancer is a disease in which cells grow out of control and form abnormal masses of cells. It is generally caused by mutations in genes that regulate the . Because of the mutations, cells with damaged DNA are allowed to divide without limits. Cancer genes can be inherited. 
      ::癌症是一种细胞无法控制地生长并形成细胞异常质量的疾病,一般是由调节细胞的基因突变引起的。由于突变,有受损DNA的细胞可以不受限制地分裂,癌症基因可以继承。

     

     

     

     

    Summary
    ::摘要

    • Mutations are essential for evolution to occur because they increase genetic variation and the potential for individuals to differ.
      ::变异对于演进至关重要,因为它们增加了遗传变异,并有可能使个人变异。
    • The majority of mutations are neutral in their effects on the organisms in which they occur.
      ::大多数突变对发生突变的生物体的影响是中性的。
    • Beneficial mutations may become more common through natural selection.
      ::通过自然选择,受益性突变可能变得更加常见。
    • Harmful mutations may cause genetic disorders or cancer.
      ::有害的突变可能导致基因紊乱或癌症。

    Review
    ::回顾

    1. Why are mutations essential for evolution to occur?
      ::为什么变异是进化的关键?
    2. What is a genetic disorder?
      ::什么是遗传障碍?
    3. What is cancer? What usually causes cancer?
      ::什么是癌症?什么通常是癌症的原因?