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  • 人口基因遗传学

    What you will learn 
    ::你会学到什么

    • How genetic changes in lead to microevolution and
      ::基因变化如何导致微进和
    • What is a gene pool
      ::什么是基因库
    • How changes in allele frequencies result in evolution  
      ::Allele频率的变化如何导致演变

    Stacks of folded blue jeans neatly organized on a display shelf.

    Jeans vs. Genes. What's the difference?
    ::Jeans和Genes有什么区别?

    Plenty. One you have for life, the other just lasts a few years. One is the basis for the passing of traits from one generation to the next. Some jeans you change frequently. But what happens when you change a gene's frequency? Essentially, evolution is a change in gene frequencies within a population.
    ::有很多。 一个你的生命,另一个只持续几年。 一个是基因从一代传到下一代的基础。 一些你经常改变的牛仔裤。 但是,当你改变基因频率时会发生什么? 从根本上说,进化是一个人口中基因频率的变化。

    Genes in Populations
    ::人口中的基因

    knew that heritable variations are needed for evolution to occur. However, he knew nothing about Mendel’s laws of genetics . Mendel’s laws were rediscovered in the early 1900s. Only then could scientists fully understand the process of evolution. We now know that variations of traits are heritable. These variations are determined by different . We also know that evolution is due to a change in alleles over time. How long a time? That depends on the scale of evolution.
    ::然而,他却对门德尔的遗传法则一无所知。 门德尔的法律在19世纪初才被重新发现。 只有那时科学家才能完全理解进化过程。 我们现在知道变异的特性是可以遗传的。 这些变异是由不同的因素决定的。我们也知道演化是随着时间推移而变化的。多久?这取决于进化的规模。

    • Microevolution occurs over a relatively short period of time within a population or . The Grants observed this level of evolution in Darwin’s finches.
      ::微变发生在人口或人口内部相对较短的一段时期内。 补助金观察到达尔文角的这种演变程度。
    • Macroevolution occurs over geologic time above the level of the species. The reflects this level of evolution. It results from microevolution taking place over many generations.
      ::巨变发生在高于物种水平的地质时间上,反映了这种进化水平,产生于代代相传的微变。

    Remember that individuals do not evolve. Their genes do not change over time. The unit of evolution is the population. A population consists of organisms of the same species that live in the same area. In terms of evolution, the population is assumed to be a relatively closed group. This means that most mating takes place within the population. The science that focuses on evolution within populations is population genetics . It is a combination of evolutionary theory and Mendelian genetics.
    ::记住个人不会进化,他们的基因不会随时间而变化。进化的单位是人口。一个人口由同一物种的有机体组成,它们生活在同一个区域。从进化的角度来看,人口被假定为一个相对封闭的群体。这意味着大多数交配发生在人口内部。关注人口内部进化的科学是人口遗传学。这是进化理论和门德勒遗传学的结合。

    Gene Pool
    ::Gene Gene 库

    The genetic makeup of an individual is the individual’s genotype . A population consists of many genotypes. Altogether, they make up the population’s gene pool. The gene pool consists of all the genes of all the members of the population. For each gene, the gene pool includes all the different alleles for the gene that exist in the population. For a given gene, the population is characterized by the frequency of the different alleles in the gene pool.
    ::个人的基因构成是个人的基因型。 人口由许多基因型组成。 总的来说,他们构成人口的基因库。 基因库由人口所有成员的所有基因组成。 对于每个基因组,基因库包括人口中存在的基因的所有不同异征。 对于特定基因组,人口特征是基因库中不同异系的频率。

    Allele Frequencies
    ::千秋千秋千金

    Allele frequency is how often an allele occurs in a gene pool relative to the other alleles for that gene. Look at the example in the Table . The population in the table has 100 members. In a sexually reproducing species, each member of the population has two copies of each gene. Therefore, the total number of copies of each gene in the gene pool is 200. The gene in the example exists in the gene pool in two forms, alleles A and a . Knowing the genotypes of each population member, we can count the number of alleles of each type in the gene pool. The table shows how this is done.
    ::相较于该基因的基因库中,异频频率是指该基因在基因库中相对于其他基因群中发生异变的频率。请看表中的例子。表中的人口有100名成员。在性繁殖的物种中,每个人口成员各有两份基因。因此,基因库中每个基因的复制件总数是200份。该基因库中的基因以两种形式存在于基因库中:A类和a类。了解每个人口组的基因类型,我们可以计算基因库中每种类型的异变的数目。表格显示了如何做到这一点。

    Genotype Number of Individuals in the Population with that Genotype Number of Allele A Contributed to the Gene Pool by that Genotype Number of Allele a Contributed to the Gene Pool by that Genotype
    AA 50 50 × 2 = 100 50 × 0 = 0
    Aa 40 40 × 1 = 40 40 × 1 = 40
    aa 10 10 × 0 = 0 10 × 2 = 20
    Totals 100 140 60

    Let the letter p stand for the frequency of allele A . Let the letter q stand for the frequency of allele a . We can calculate p and q as follows:
    ::让字母 p 代表 Altele A 的频率。 让字母 q 代表 A a 的频率。 我们可以计算p 和 q 如下:

    • p = number of A alleles/total number of alleles = 140/200 = 0.7
      ::p = alleles 数/ alleles 总数= 140/200 = 0.7
    • q = number of a alleles/total number of alleles = 60/200 = 0.3
      ::q = 排量数/排量总数= 60/200 = 0.3
    • Notice that p + q = 1.
      ::注意到p+q=1。

    Evolution occurs in a population when allele frequencies change over time. The example below shows how allele frequencies change in a population of sparrows over several generations due to external influences. It demonstrates the effect of a predatory that chooses brown-colored sparrows because they are easier to find in a given environment and a parasitic insect to which the yellow-colored sparrows are particularly vulnerable.
    ::进化发生在一个人口群体中,当Altele频率随时间变化时。下面的例子显示了由于外部影响,若干代麻雀群中的异性频率是如何变化的。它展示了食肉动物选择棕色麻雀的影响,因为它们更容易在黄色麻雀特别易受其影响的特定环境和寄生虫中找到。

    How do allele frequencies change in a population?
    ::人口频率如何变化?

     

     

    Check your understanding!
    ::检查你的理解!

     

     

     

     

    Summary
    ::摘要

    • Microevolution occurs over a short period of time in a population or species. Macroevolution occurs over geologic time above the level of the species.
      ::在一个种群或物种中,在短时期内发生微变,在超过物种水平的地质时间内发生微变。
    • The population is the unit of evolution.
      ::人口是进化的单位。
    • A population’s gene pool consists of all the genes of all the members of the population.
      ::人口基因库由人口所有成员的所有基因组成。
    • For a given gene, the population is characterized by the frequency of different alleles in the gene pool.
      ::对于某一基因而言,人口特征是基因库中不同基因源的频率。

    Review
    ::回顾

    1. Compare microevolution to macroevolution.
      ::将微观进化与宏观进化作比较。
    2. Why are populations, rather than individuals, the units of evolution?
      ::为什么人口而不是个人是进化的单位?
    3. What is a gene pool?
      ::什么是基因库?
    4. Assume that a population of 50 individuals has the following numbers of genotypes for a gene with two alleles, B and b : BB = 30, Bb = 10, and bb = 10. Calculate the frequencies of the two alleles in the population’s gene pool.
      ::假定50个人口的人口具有下列人数的基因型,即B和B两个等同基因的基因:BB=30,Bb=10,bb=10。bb=10。 计算人口基因库中两个等同基因的频率。