Section outline

  • General

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  • 遗传联系

    What you will learn
    ::你会学到什么

    • Linked genes and how they are inherited
      ::连接的基因及其继承方式
    • How the frequency of crossing over can help construct a genetic map
      ::过境频率如何帮助绘制基因图?

    A close-up of linked metal chain segments against a blurred natural background.

    What does it mean to be linked?
    ::连接意味着什么?

    For a chain, the above image may suggest a certain type of linkage. For genes , it might suggest that they are very hard to separate. If this is the case, what does this mean in terms of human traits? Can you think of any human traits that tend to be inherited together?
    ::对于链条来说,上述图像可能暗示某种类型的关联。对于基因来说,它可能表明它们很难分离。如果是这样,那么从人的特征来说,这意味着什么?你能想到任何人类的特征,这些特征往往会一起继承吗?

    Linkage
    ::链接

    Genes that are located on the same are called linked genes . for these genes tend to segregate together during unless they are separated by crossing over. Crossing over occurs when two homologous chromosomes exchange genetic material during meiosis I. The closer together two genes are on a chromosome, the less likely their alleles will be separated by crossing over as shown in the Figure . 
    ::位于同一处的基因被称为关联基因。 因为这些基因往往在通过交叉途径隔开时相互分离。 当两种同质染色体在美化一期间交换遗传物质时,就会发生交叉。 两种基因越接近于一种染色体,越有可能通过交叉途径分离它们的异系物,如图所示。

    Chromosomal crossing over demonstrating linked genes during meiosis.
    Linked genes are inherited together as their alleles are located close to each other and are less likely to be separated by crossing over.

    Linkage explains why certain characteristics are frequently inherited together. For example, genes for hair color and eye color are linked, so certain hair and eye colors tend to be inherited together, such as blonde hair with blue and brown hair with brown eyes. What other human traits seem to occur together? Do you think they might be controlled by linked genes?
    ::链接解释了为什么某些特征经常被一起继承。 比如,头发颜色和眼睛颜色的基因是联系在一起的,因此某些头发和眼睛的颜色往往是一起继承的,比如金发和蓝色头发,棕色头发和棕色眼睛。其他人类特征似乎也同时出现。你认为它们可能由有联系的基因来控制吗?

    Sex-Linked Genes
    ::性链接的基因

    Genes located on the sex chromosomes are called sex-linked genes . Most sex-linked genes are on the X chromosome because the Y chromosome has relatively few genes. Strictly speaking, genes on the X chromosome are X-linked genes , but the term sex-linked is often used to refer to them.
    ::存在于性染色体上的基因被称为与性相关的基因。 大部分与性相关的基因都存在于X染色体上,因为Y染色体的基因相对较少。 严格地说,X染色体上的基因是与性相关的基因,但与性相关的术语常常被用来指它们。

    Mapping Linkage
    ::绘图联系

    Linkage can be assessed by determining how often crossing over occurs between two genes on the same chromosome. Genes on different (nonhomologous) chromosomes are not linked. They assort independently during meiosis, so they have a 50 percent chance of ending up in different gametes . If genes show up in different gametes less than 50 percent of the time (that is, they tend to be inherited together), they are assumed to be on the same (homologous) chromosome. They may be separated by crossing over, but this is likely to occur less than 50 percent of the time. The lower the frequency of crossing over, the closer together on the same chromosome the genes are presumed to be. Frequencies of crossing over can be used to construct a linkage map like the one in the  Figure . A linkage map shows the locations of genes on a chromosome.
    ::可以通过确定同一染色体上两种基因之间的交叉频率来评估联系。 不同( 非血色) 染色体上的基因没有连接。 它们独立分布, 所以它们有50%的概率出现在不同的调子中。 如果基因在不同的调子中出现不到50%的时间( 也就是说, 它们往往被一起继承) , 它们被假定在相同的( 血色) 染色体上。 它们可能通过交叉而分离, 但可能不到50%的时间。 跨越频率越低, 基因在相同的染色体上相较近, 被推定为越近。 交叉的细数可以用来构建像图中那样的连接图。 连接图显示染色体上的基因的位置 。

    Linkage map of the Human X chromosome showing gene locations and associated disorders.
    Linkage Map for the Human X Chromosome. This linkage map shows the locations of several genes on the X chromosome. Some of the genes code for normal proteins. Others code for proteins that are associated with genetic disorders. Which pair of genes would you expect to have a lower frequency of crossing over: the genes that code for hemophilia A and G6PD deficiency, or the genes that code for Protan and Xm?
    DID YOU KNOW?
    Alfred Henry Sturtevant, an American geneticist, constructed the first genetic map of a chromosome in 1913. He was the first to propose that genes are arranged on a chromosome in an order that can be mapped by observing the frequency of crossing over. His genetic mapping method is still used today, among other modern techniques.
     

     

     

    Summary
    ::摘要

    • Linked genes are located on the same chromosome.
      ::链接基因位于同一个染色体上。
    • Sex-linked genes are located on a sex chromosome, and X-linked genes are located on the X chromosome.
      ::性相关基因位于性染色体上,X相关基因位于X染色体上。
    • The frequency of crossing over between genes is used to construct linkage maps that show the locations of genes on chromosomes.
      ::基因之间的交叉频率被用来绘制连接图,显示染色体上的基因位置。

    Review
    ::回顾

    1. What are linked genes?
      ::什么是关联基因?
    2. Explain how you would construct a linkage map for a human chromosome. What data would you need?
      ::解释您如何为人类染色体构建链接地图。 您需要哪些数据 ?
    3. People with red hair usually have very light skin. What might be a genetic explanation for this observation?
      ::红发人通常皮肤很浅,这种观察的遗传解释是什么?
    4. How often does crossing over occur between non-linked genes? Explain your answer.
      ::无关联基因之间多久跨越一次?解释一下答案。