章节大纲

  • 常规

    全部折叠 展开全部

  • 变异

    What you will learn
    ::你会学到什么

    • What are mutations and how are they caused
      ::什么是变异 以及它们是如何引起的
    • Two major categories of mutations
      ::两大类突变
    • What are chromosomal alterations and its types
      ::哪些是染色体变化及其类型
    • Point mutations and their effects
      ::点突变及其效果

    An albino alligator resting on a rock by the water.

    What causes albinism?
    ::白化病的原因是什么?

    This rare albino alligator must have the specific "instructions," or , to have this quality. The cause of albinism is a mutation in a gene for melanin , a found in skin and . Such a mutation may result in no melanin production at all or a significant decline in the amount of melanin.
    ::这种稀有的白化病鳄鱼必须具有特定的“指示 ” , 或者, 才能具有这样的质量。 白化病的原因是在美兰素基因中突变,皮肤和皮肤中发现的。 这种突变可能不会导致梅兰素生产,或者梅兰宁的数量会大幅下降。

    Mutations
    ::变异

    A change in the sequence of bases in DNA is called a mutation . Does the word mutation make you think of science fiction and bug-eyed monsters? Think again. Everyone has mutations. In fact, most people have dozens or even hundreds of mutations in their DNA. Mutations are essential for evolution to occur. They are the ultimate source of all new genetic material - new - in a . Although most mutations have no effect on the organisms in which they occur, some mutations are beneficial. Even harmful mutations rarely cause drastic changes in organisms.
    ::DNA基数序列的变化被称为突变。 突变这个词是否让你想到科幻小说和虫眼怪物? 再想想。 每个人都有突变。 事实上, 大多数人的DNA中都有几十甚至数百个变异。 变异对于进化至关重要。 变异是所有新基因材料的最终来源 - - - - - - - - - - - - 一个新的 - - - - - 在一种情况下。 虽然大多数变异对发生变异的有机体没有影响, 但有些变异是有用的。 即使是有害的变异也很少引起生物的急剧变化 。

     

     

    Types of Mutations
    ::变音类型

    There are a variety of types of mutations. Two major categories of mutations are germline mutations and somatic mutations .
    ::突变有多种类型,两种主要突变类型是子宫突变和体突变。

    • Germline mutations occur in gametes . These mutations are especially significant because they can be transmitted to offspring and every in the offspring will have the mutation.
      ::这些突变特别重要,因为它们可以传给后代,每个后代都会有突变。
    • Somatic mutations occur in other cells of the body. These mutations may have little effect on the organism because they are confined to just one cell and its daughter cells . Somatic mutations cannot be passed on to offspring.
      ::体外突变发生在身体的其他细胞中。这些突变可能对有机体没有多大影响,因为它们只局限在一个细胞及其子细胞中,不能将体外突变传给后代。

    Mutations also differ in the way that the genetic material is changed. Mutations may change the structure of a or just change a single nucleotide .
    ::基因物质改变的方式也不同,变异可能改变一种核素的结构,或只是改变一种核素。

    Chromosomal Alterations
    ::染色体改变

    Chromosomal alterations are mutations that change chromosome structure. They occur when a section of a chromosome breaks off and rejoins incorrectly or does not rejoin at all.
    ::染色体的改变是改变染色体结构的突变。 当染色体的某一部分断裂并错误地重新加入或根本不重新加入时, 染色体的改变就会发生。

    Possible types of mutations in chromosomes include:
    ::染色体中可能发生的突变类型包括:

    1. Deletion: When a segment of DNA is lost, so there is a missing segment in the chromosome. These usually result in many genes missing from the chromosome.
      ::删除: 当一个DNA部分丢失时, 染色体中就有一个缺失的部分。 这通常会导致染色体中缺少许多基因。
    2. Duplication: When a segment of DNA is repeated, creating a longer chromosome. These usually result in multiple copies of genes in the chromosome.
      ::重复: 当重迭一个DNA段时, 会产生更长的染色体。 这通常会导致染色体中基因的多个复制件 。
    3. Inversion: When a segment of DNA is flipped and then reattached to the same chromosome.
      ::反向:当DNA的某一部分被翻转,然后重新连接到同一种染色体时。
    4. Insertion: When a segment of DNA from one chromosome is added to another, unrelated chromosome.
      ::插入:当一个染色体的DNA部分添加到另一个无关的染色体中时。
    5. Translocation: When two segments from different chromosomes change positions.
      ::变换位置:当来自不同染色体的两个区段改变位置时。

    Possible ways these mutations can occur are illustrated in the  Figure .
    ::图1说明了这些突变的可能发生方式。

    Chromosomal mutations: deletion, duplication, inversion, insertion, and translocation.
    Chromosomal Alterations. Chromosomal alterations are major changes in the genetic material.

    Chromosomal alterations are very serious. They often result in the death of the organism in which they occur. If the organism survives, it may be affected in multiple ways.
    ::染色体的改变非常严重,往往导致发生染色体的有机体死亡,如果生物体存活下来,可能会以多种方式受到影响。

    What are the changes in chromosomal structure due to chromosomal alterations?
    ::染色体改变对染色体结构有何变化?

    Point Mutations
    ::点变数

    A point mutation is a change in a single nucleotide in DNA. This type of mutation is usually less serious than a chromosomal alteration. An example of a point mutation is a mutation that changes the codon UUU to the codon UCU . Point mutations can be silent, missense, or nonsense mutations, as shown in the  Table . These types of point mutations are also known as substitutions. Their effects depend on how they change the . 
    ::点突变是DNA中单核核酸的改变。 这种突变通常比染色体变异不严重。 点突变的一个例子是, 点突变会将codon UUU 改变为codon UCU。 点突变可以是静音、 missense 或无稽变异, 如表所示。 这些点变异也被称为替代。 它们的效果取决于它们如何改变 。

    Type Description Example Effect
    Silent mutated codon codes for the same amino acid CAA (glutamine) → CAG (glutamine) none
    Missense mutated codon codes for a different amino acid CAA (glutamine) → CCA (proline) variable
    Nonsense mutated codon is a premature stop codon CAA (glutamine) → UAA (stop) usually serious

    Frameshift Mutations
    ::框架图变变

    A frameshift mutation  (also a type of point mutation) includes a deletion or insertion of one or more nucleotides that changes the reading frame of the base sequence. Deletions remove nucleotides, and insertions add nucleotides. Consider the following sequence of bases in :
    ::框架转移突变(也是一种点突变类型)包括删除或插入一个或多个核素,以改变基准序列的读数框架。删除去除核素,插入添加核素。考虑以下基数序列:

    AUG-AAU-ACG-GCU = start-asparagine-threonine-alanine
    ::AUG-AAAU-ACG-GCU = 开始的paraggine-threonine-aline

    Now, assume an insertion occurs in this sequence. Let’s say an A nucleotide is inserted after the start codon AUG :
    ::现在,假设在这个序列中插入一个插件。让我们假设一个核核酸在开始后插入到 AUG 之后:

    AUG-AAA-UAC-GGC-U = start-lysine-tyrosine-glycine
    ::AUG-AAAA-UAC-GGC-U

    Even though the rest of the sequence is unchanged, this insertion changes the reading frame and thus all of the codons that follow it. As this example shows, a frameshift mutation can dramatically change how the codons in mRNA are read. This can have a drastic effect on the protein product.
    ::尽管其余的顺序没有变化, 但插入会改变读数框架, 从而改变随之而来的所有codon。 正如这个例子所显示的, 框架转换突变可以显著改变 mRNA 中的codon 是如何阅读的。 这可能会对蛋白质产品产生巨大影响 。

    What effect do the different point mutations have on an amino acid sequence?
    ::不同点突变对氨基酸序列有何影响?

    DID YOU KNOW?
    Cystic Fibrosis is a caused by mutations in the gene encoding CFTR (cystic fibrosis transmembrane regulator) protein. Most of the mutations that result in the disorder are point mutations. 
     

    Albinism
    ::白白化病

    Albinism  is  not commonly seen in nature because the change in pigmentation is often a disadvantage to organisms in their natural environment. The lack of pigmentation can make the albino organism more vulnerable and an easier target to predators since organisms with albinism, for instance, cannot easily camouflage themselves into their environment. As a result, an albino alligator like the one depicted above may not live long enough to survive and reproduce due to being more vulnerable and easier prey to predators. 
    ::白化病在自然界并不常见,因为色素的改变往往对自然环境中的有机体不利,缺乏色素会使白化生物更易受到伤害,更容易成为食肉动物的目标,因为例如白化生物无法轻易地将自己伪装到环境中去,因此,像上文描述的白化类鳄鱼可能活不到生存和繁殖的足够长的时间,因为食肉动物更容易和容易受食肉动物的捕食。

     

     

     

    Summary
    ::摘要

    • Germline mutations occur in gametes. Somatic mutations occur in other body cells.
      ::发热突变发生在数位数中,体突变发生在其他身体细胞中。
    • Chromosomal alterations are mutations that change chromosome structure.
      ::染色体改变是突变 改变染色体结构
    • Point mutations change a single nucleotide.
      ::点突变改变了单核酸
    • Frameshift mutations are additions or deletions of nucleotides that cause a shift in the reading frame.
      ::框架变异是核糖核酸的增减,导致阅读框架的改变。

    Review
    ::回顾

    1. Identify three types of chromosomal alterations.
      ::查明三种染色体变化。
    2. Distinguish among silent, missense, and nonsense point mutations.
      ::区分沉默, 小姐, 和无稽之谈 点突变。
    3. What is a frameshift mutation? What causes this type of mutation?
      ::什么是轮廓变异?什么是这种变异的原因?
    4. Assume that a point mutation changes the codon AUU to AUC. Why is this a silent mutation?
      ::假设一个点变异会把AUU的codon改变为AUC。 为什么这是静态变异?
    5. Look at the following mutation: AUG-GUC-CCU-AAA → AUG-AGU-CCC-UAA-A. The base A was inserted following the start codon AUG. Describe how this mutation affects the encoded amino acid sequence.
      ::AUG-GUC-CCU-AAA AUG-AG-AGU-CCC-UAAAAAAAAAAAAUG-AUGU-AGU-ACUAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
    6. Compare and contrast germline mutations and somatic mutations.
      ::比较和对比子系突变和体突变