Section outline

  • General

    Collapse all Expand all

  • 遗传变异

    What you will learn
    ::你会学到什么

    • How results in genetic variation
      ::如何导致遗传变异
    • The role of crossing over in creating unique combinations of genes
      ::跨越边界在创造独特的基因组合方面的作用

    Diverse characters representing genetic variation and its role in evolution.

    What helps ensure the survival of a species?
    ::什么能帮助确保物种的生存?

    Genetic variation. It is this variation that is the essence of evolution. Without genetic differences among individuals, "survival of the fittest" would not be likely. Either all survive, or all perish.
    ::基因变异:这种变异是进化的精髓。没有个人之间的基因差异,“适者生存”不太可能。要么全部生存,要么全部灭亡。

    Genetic Variation
    ::遗传变异

    Sexual reproduction results in infinite possibilities of genetic variation. In other words, sexual reproduction results in offspring that are genetically unique. They differ from both parents and also from each other. This occurs for a number of reasons.
    ::性生殖造成基因变异的无限可能性,换句话说,性生殖导致遗传上独一无二的后代,与父母和父母不同,原因很多。

    • When homologous chromosomes form pairs during prophase I of I, crossing over can occur. Crossing over is the exchange of genetic material between homologous chromosomes. It results in new combinations of genes on each .
      ::当同族染色体在I期的第一阶段形成一对同族染色体时,可能会发生交叉。交叉是同族染色体之间的基因材料交换。这导致每种染色体的基因新组合。
    • When divide during meiosis, homologous chromosomes are randomly distributed to daughter cells , and different chromosomes segregate independently of each other. This is called independent assortment . It results in gametes that have unique combinations of chromosomes.
      ::当介质分裂时,同族染色体会随机分布到女儿的细胞中,而不同的染色体会相互分离。这被称为独立分类。它导致有独特的染色体组合的调子。
    • In sexual reproduction, two gametes unite to produce offspring. But which two of the millions of possible gametes will it be? This is likely to be a matter of chance. It is obviously another source of genetic variation in offspring. This is known as random fertilization .
      ::在性生殖方面,两个调子结合来产生后代。 但是,在几百万种可能的调子中,哪两个会产生后代? 这很可能是偶然的。 这显然是后代遗传变异的另一个来源。 这被称为随机受孕。

    All of these mechanisms working together result in an amazing amount of potential variation. Each human couple, for example, has the potential to produce more than 64 trillion genetically unique children. No wonder we are all different!
    ::所有这些机制一起工作,都产生了惊人的潜在差异,例如,每对人类夫妇都有可能产生64万亿多个基因独特的儿童。 难怪我们都不同!

    Crossing Over
    ::跨越

    Crossing over occurs during prophase I, and it is the exchange of genetic material between non-sister chromatids of homologous chromosomes. Recall during prophase I, homologous chromosomes line up in pairs, gene-for-gene down their entire length, forming a configuration with four chromatids, known as a tetrad . At this point, the chromatids are very close to each other and some material from two chromatids switch chromosomes, that is, the material breaks off and reattaches at the same position on the homologous chromosome. This exchange of genetic material can happen many times within the same pair of homologous chromosomes, creating unique combinations of genes, as shown in the animation below. This process is also known as recombination .
    ::在第一期期间交叉发生,这是同质染色体的非姐妹染色体之间基因材料的交换。在第一期期间回顾,同质染色体排成一对,整个长度以基因换基因,形成四种染色体(称为四色相)的组合。此时,染色体彼此非常接近,并且来自两个染色体开关染色体的一些材料,即,同质染色体上的物质断裂和重新连接。这种基因材料的交换可以多次发生在同一对同质染色体内,创造独特的基因组合,正如以下动画所示。这一过程也被称为重组。

    Independent Assortment and Random Fertilization
    ::独立组分和随机授肥

    In humans, there are over 8 million configurations in which the chromosomes can line up during metaphase I of meiosis. It is the specific processes of meiosis, resulting in four unique haploid cells, that result in these many combinations. This independent assortment, in which the chromosome inherited from either the father or mother can sort into any gamete, produces the potential for tremendous genetic variation. Together with random fertilization, more possibilities for genetic variation exist between any two people than the number of individuals alive today. Sexual reproduction is the random fertilization of a gamete from the female using a gamete from the male. In humans, over 8 million (2 23 ) chromosome combinations exist in the production of gametes in both the male and female. A cell, with over 8 million chromosome combinations, fertilizes an egg cell, which also has over 8 million chromosome combinations. That is over 64 trillion unique combinations, not counting the unique combinations produced by crossing over. In other words, each human couple could produce a child with over 64 trillion unique chromosome combinations!
    ::在人类中,有超过800万个配置的染色体可以在梅氏1的元子阶段排成一列。这是梅氏病的具体过程,导致四个独特的折合细胞,导致这些众多的组合。这种独立的分解,从父亲或母亲继承的染色体可以分解成任何组合体,产生巨大的基因变异的可能性。与随机授精一起,任何两个人之间的基因变异的可能性都比今天活着的人数多。性生殖是女性使用男性的调子随机施肥。在人类中,有超过800万个(223)个染色体组合存在于男女的调合体中。一个细胞,有超过800万个染色体的组合,使一个蛋细胞发生发酵,它也拥有超过800万个染色体的组合。这是超过64万亿个独特的组合,并不包括通过交叉生成的独特组合。换言之,每个人类夫妇可以产生一个超过64万亿个独特的染色体组合的孩子。

     

     

     

    DID YOU KNOW?
    Single Nucleotide Polymorphisms (SNPs) are the most common type of genetic variation among people. SNPs involve variation in a single base pair that occurs naturally in the genome .
     

    Summary
    ::摘要

    • Sexual reproduction has the potential to produce tremendous genetic variation in offspring.
      ::性生殖有可能在后代中产生巨大的遗传变异。
    • This variation is due to independent assortment and crossing over during meiosis, and random union of gametes during fertilization.
      ::之所以出现这种差异,是因为在梅思蒂病期间独立分布和跨越边界,以及在受孕期间随机组合调子。

    Review
    ::回顾

    1. What is crossing over and when does it occur?
      ::什么是跨越边界,何时发生?
    2. Describe how crossing over, independent assortment, and random fertilization lead to genetic variation.
      ::说明跨越、独立的分类和随机授精如何导致遗传变异。
    3. How many combinations of chromosomes are possible from sexual reproduction in humans?
      ::有多少染色体的组合 从人类的性生殖中可以实现?
    4. Create a diagram to show how crossing over occurs and how it creates new gene combinations on each chromosome.
      ::创建一个图表, 显示如何交叉交叉, 以及如何在每一个染色体上创造新的基因组合 。