Section outline

  • General

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  • 演变力量的演变

    What you will learn 
    ::你会学到什么

    • What are the forces of evolution
      ::进化的力量是什么?
    • What is and how does it happen
      ::是什么以及它是如何发生的

    A lever with green labeled 'CHANGE' and red labeled 'SAME', symbolizing evolution.

    How do a population's genes change?
    ::人口基因如何改变?

    Remember, without change, there cannot be evolution. Together, the forces that change a population's gene frequencies are the driving mechanisms behind evolution.
    ::记住,没有变化,就不可能有进化。 共同改变人口基因频率的力量是进化背后的驱动机制。

    Forces of Evolution
    ::演变力量的演变

    The conditions for Hardy-Weinberg equilibrium are unlikely to be met in real . The Hardy-Weinberg theorem also describes populations in which allele frequencies are not changing. By definition, such populations are not evolving. How does the theorem help us understand evolution in the real world?
    ::Hardy-Weinberg 平衡的条件不可能在现实中得到满足。 Hardy-Weinberg 理论也描述了所有频率没有变化的人口。根据定义,这些人口没有变化。 理论如何帮助我们理解现实世界的演变?

    From the theorem, we can infer factors that cause allele frequencies to change. These factors are the "forces of evolution." There are four such forces: , , genetic drift, and .
    ::从理论中,我们可以推断出导致所有频率变化的因素。这些因素是“进化力量”。有四种这种力量: 、 、 、 、 基因漂移 、 和 。

    Mutation
    ::变异

    Mutations create new genetic variations in a gene pool . It is how all new first arise. In sexually reproducing , the mutations that matter for evolution are those that occur in gametes . Only these mutations can be passed to offspring. For any given gene, the chance of a mutation occurring in a given gamete is very low. Thus, mutations alone do not have much effect on allele frequencies. However, mutations provide the needed for other forces of evolution to act.
    ::突变在基因库中创造了新的基因变异。 所有的突变都是如何出现的。 在性再生中, 进化重要的突变是在数子体中发生的变异。 只有这些变异可以传给后代。 对于任何特定的基因来说, 某个基因中发生突变的可能性非常低。 因此, 单是突变不会对异变频率产生多大影响。 但是, 突变提供了其他进化力量采取行动所需的条件 。

    Gene Flow
    ::基因流动

    Gene flow occurs when individuals move into or out of a population. If the rate of is high, this can have a significant effect on allele frequencies. The allele frequencies of both the population they leave and the population they enter may change.
    ::当个人进入或离开人口时,即发生基因流动,如果人口比率高,则可能对Alele频率产生重大影响,离开人口和进入的人口的Alle频率都可能发生变化。

    For example, wind or can carry pollen or seeds from one plant population to another. In baboon troops or wolf packs, juvenile males may leave the group to find mates and establish separate populations. Human history includes countless migrations; gene flow continues to mix gene pools and cause microevolutionary changes.
    ::例如,风能或能够把花粉或种子从一个植物群体带到另一个植物群体;在浣熊部队或狼群中,少年男性可能离开该群体寻找伴侣,建立不同的人口;人类历史包括无数移徙;基因流动继续混合基因库,并造成微进变化。

    Genetic Drift
    ::遗传漂流

    Genetic drift is a random change in allele frequencies that occurs in a small population. When a small number of parents produce just a few offspring, allele frequencies in the offspring may differ, by chance, from allele frequencies in the parents.
    ::遗传漂移是少数人口中异频频率的随机变化。 当少数父母只生几个后代时,后代的异频可能偶然与父母的异频不同。

    This is like tossing a coin. If you toss a coin just a few times, you may, by chance, get more or less than the expected 50 percent heads or tails. In a small population, you may also, by chance, get different allele frequencies than expected in the next generation. In this way, allele frequencies may drift over time.
    ::这就像抛硬币一样。如果你扔硬币几次,你可能会偶然得到超过或少于预期的50%头部或尾部。在一小部分人中,你也可能偶然得到不同于下一代人预期的异频。这样,所有频率可能会随着时间流逝而变化。

    There are two special conditions under which genetic drift occurs. They are called bottleneck effect and founder effect .
    ::基因漂移有两个特殊条件,称为瓶颈效应和创建效应。

    1. Bottleneck effect occurs when a population suddenly gets much smaller. This might happen because of a natural disaster such as a forest fire or a volcanic eruption (see the Figure ). By chance, allele frequencies of the survivors may be different from those of the original population.
      ::当人口突然变小时,就会产生瓶颈效应。 这可能因为森林火灾或火山爆发等自然灾害而发生(见图 ) 。 偶然情况下,幸存者的频率可能与原始人口不同。
    Genetic Drift: Initial Population, Bottleneck Event, Survivors, And New Population.
    The bottleneck effect: The seal population on the island is reduced due to a volcanic eruption. The surviving individuals form the new population with different allele frequencies than the original population.
    1. Founder effect occurs when a few individuals start, or found, a new population. By chance, allele frequencies of the founders may be different from allele frequencies of the population they left. An example is described in the Figure .
      ::创建者的作用是当几个人开始或发现新的人口时发生。 偶然情况下,创建者的所有频率可能不同于他们离开的人口的所有频率。 图中描述了一个例子。
    Depicts bottleneck and founder effects using colored balls and lizards on islands.
    The founder effect: A few lizards are isolated from the main population of lizards from a continent by chance and drift to a distant island. Their numbers gradually increase on the new island, but the allele frequencies of the new population are different compared to the original population.

    Founder Effect in the Amish Population
    ::对阿米什人口的影响

    A horse-drawn buggy in a rural setting, representative of Amish transportation.

    Who Are the Amish?
    ::阿米什人是谁?

    • There are almost 250,000 Amish people in the U.S. and Canada today. They live in small rural communities, mainly in Ohio, Pennsylvania, and New York.
      ::今天,美国和加拿大有近25万阿米什人,他们生活在小农村社区,主要是俄亥俄州、宾夕法尼亚州和纽约。
    • The present Amish population grew from 200 founders, who came to the U.S. from Germany and Switzerland in the mid-1700s.
      ::目前的阿米什人口从200个创始人增长,他们于1700年代中期从德国和瑞士来到美国。
    • Since then, the Amish have followed a simple lifestyle. For example, they do not own cars and instead travel by horse and buggy.
      ::从那时起,阿米什人就遵循简单的生活方式,例如,他们不拥有汽车,而是骑马和骑马旅行。
    • Amish people also rarely intermarry with people outside the Amish population.
      ::阿米人也很少与阿米什人以外的人通婚。
    Comparison of hands showing normal fingers and fingers with extra digits due to a condition.

    Founder Effect and the Amish Gene pool
    ::创建者效果和 Amish Genene 池池

    • One of the original 200 Amish founders carries a recessive allele for a rare condition. Called Ellis-van Creveld syndrome, the condition is a type of dwarfism. People with the syndrome have extra fingers and short limbs.
      ::最初的200个阿米什族创始人中,有1个有着极罕见条件的休眠异象。 被称为埃利斯-范·克雷维尔德综合症(Ellis-van Creveld ) , 病症是一种侏儒症。 患有该综合症的人有额外的手指和短肢。
    • Today, the Amish population has far more cases of this syndrome than any other population in the world.
      ::今天,阿米什人患这种综合症的病例远远多于世界上任何其他人。

      

     

     

     

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

     

     

     

    Summary
    ::摘要

    • There are four forces of evolution: mutation, gene flow, genetic drift, and natural selection.
      ::有四种进化力量:突变、基因流动、基因漂移和自然选择。
    • Mutations create new genetic variations in a gene pool.
      ::突变在基因库中创造了新的基因变异。
    • Gene flow and genetic drift alter allele frequencies in a gene pool.
      ::基因流动和遗传漂移改变基因库中的异频频率。

    Review
    ::回顾

    1. Identify the four forces of evolution.
      ::确定四种进化力量。
    2. Why is mutation needed for evolution to occur, even though it usually has little effect on allele frequencies?
      ::为什么进化需要突变才能发生呢? 尽管突变通常不会对Allee频率产生什么影响?
    3. What is founder effect? Give an example.
      ::什么是创建效果?举个例子。
    4. Explain why genetic drift is most likely to occur in a small population.
      ::解释为什么基因漂移最可能发生在少数人口中。