10.34 变异和基因流动 -- -- 高级
Section outline
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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。Causes of Microevolution: Mutation and Gene Flow
::微进原因:变异和基因流动As discussed previously, – random, accidental changes in the sequence of nucleotides in – are the original sources of . Only mutations can create new – new raw material for . UV or ionizing radiation, chemicals, and constantly generate mutations in a gene pool , destabilizing genetic equilibrium and creating the potential for adaptation to changing environments. However, both rates of mutation and their effects on the fitness of the organism vary.
::如前文所述,核糖核酸序列的随机意外变化 — — 是最初的源头。 只有突变才能创造新的原材料 — — 用于紫外线或电离辐射、化学物质,并在基因库中不断产生突变,破坏基因平衡的稳定,并创造适应变化环境的潜力。 然而,突变速度及其对有机体健康的影响各不相同。In , most mutations occur in body and do not affect eggs and ; these are lost when the individual dies and usually do not affect evolution. Only mutations in gamete-producing cells can become part of the gene pool. The rate at which mutations enter the gene pool is low, due to DNA “proofreading” and repair - and the extensive amount of DNA which does not code for . Mutations which do change nucleotide sequences in functional genes may also have no effect (because the is redundant - multiple codons code for the same amino acid), or very little effect, if the amino acid is not located in a critical part of the protein.
::大多数突变发生在身体中,不会影响卵和;当个人死亡时,这些变异就会消失,而且通常不会影响进化。只有果冻产细胞中的变异才能成为基因库的一部分。由于DNA“校对”和修复,突变进入基因库的速度很低,而且DNA数量巨大,无法编码。确实改变功能性基因核糖酸序列的变异也可能没有效果(因为这种变异是多余的-同一氨基酸的多重codon代码),或者如果氨基酸不位于蛋白质的关键部分,影响很小。Occasionally, however, a single nucleotide substitution can have a major effect on a protein – as we previously saw with sickle-cell anemia . Usually, the effect of a mutation on a protein is harmful; rarely is it helpful. In the case of sickle-cell anemia, it is both – depending on the environment. Sickled cells carry oxygen much less efficiently, but prevent malaria infections. Overall, the chance that a single mutation will increase the fitness of a multicellular organism is extremely low. If the environment changes, however, the adaptive value of a new allele may change as well. Over time, mutations accumulate, providing the variation needed for natural selection.
::然而,有时,单核糖酸替代品会对蛋白质产生重大影响 — — 正如我们以前在镰状细胞贫血中看到的那样。 通常情况下,突变对蛋白质的影响是有害的,很少有帮助。 在镰状细胞贫血中,两者都是 — — 取决于环境。 被污染的细胞携带氧气的效率要低得多,但可以预防疟疾感染。 总体而言,单次突变会增加多细胞机体的适合性的可能性非常低。 但是,如果环境变化,新异性动物的适应性价值也会改变。 随着时间的推移,突变会积累,为自然选择提供所需的变异。For the small genomes of viruses and , mutations affect genes directly and generation times are short, so rates of mutation are much higher. For an in one AIDS patient, rates of viral mutation and replication are so high that in a single day, every site in the HIV genome may have experienced mutation ( Figure ). This rapid generation of new alleles challenges our best efforts at drug treatment and explains the evolution of antibiotic resistance . Because of the abundance of random, spontaneous mutations, HIV generates a large amount of raw material for natural selection and readily evolves resistance to new “environments” created by single drugs ( Figure ). Drug “cocktails,” which contain multiple anti-viral chemicals, are our effort to change the “environment” and keep up with mutation in the human-HIV evolutionary race. For microorganisms, mutation is a strong force for evolution.
::对于病毒和变异的小型基因组来说,病毒和变异直接影响到基因,而代际时间则很短,因此突变率要高得多。对于一名艾滋病患者来说,病毒突变和复制率非常高,以至于在一天之内,艾滋病毒基因组的每个地点都可能都经历了突变(图 ) 。 这种迅速产生的新异变对我们在药物治疗和解释抗生素抗药性演变方面的最佳努力提出了挑战。由于随机、自发的突变数量巨大,艾滋病毒为自然选择创造了大量原材料,并且很容易对单一药物创造的新的“环境”产生抵抗力(图 ) 。 含有多种抗病毒化学品的药物“鸡尾酒 ” , 是我们改变“环境” 和跟上人类-艾滋病毒进化种族的突变的努力。 对于微生物来说,突变是进的强大力量。HIV daughter particles are shed from an infected human T-cell host. Both HIV replication and mutation rates are so high that during a single day, the HIV population in one AIDS patient generates mutations at every site in the HIV genome. New alleles provide the potential for extremely rapid evolution, including the development of resistance to drugs.
::艾滋病毒女儿的颗粒是从受感染的人类T细胞宿主身上释放出来的。 艾滋病毒的复制和突变率都非常高,在一天的时间里,一个艾滋病患者中的艾滋病毒感染者在艾滋病毒基因组的每个地点都会产生突变。 新的异形为极端快速的演变提供了潜力,包括对药物的抗药性的发展提供了可能性。Extremely high HIV mutation rates provide many new alleles – the raw material for natural selection – in AIDS patients. This variation allows at least some mutant viruses to survive and reproduce in the changing “environments” of new drug therapies. The graph shows the effects of one type of drug: an initial decrease in the HIV population and a temporary rise in the number of human host (CD4) cells. Before long, however, mutants with alleles conferring drug resistance appear and begin to reproduce, which leads to a recovery in the HIV population. This change in allele frequencies is microevolution, caused by mutation and natural selection.
::极高的艾滋病毒突变率为艾滋病病人提供了许多新的异质 — — 即自然选择的原材料 — — 。 这种变异至少允许某些变异病毒在新的药物疗法不断变化的“环境”中生存和繁殖。 图表显示了一种药物的影响:艾滋病毒的初始人口减少和人类宿主细胞(CD4)的暂时增加。 然而,不久之后,带有产生抗药性的异端的变异体出现并开始繁殖,从而导致艾滋病毒人口的复苏。 这种变异病毒频率的变化是微变,是由突变和自然选择造成的。For all organisms, mutations are the ultimate source of genetic variation. For a population, however, the immigration or emigration of individuals or gametes may also add to or subtract from a gene pool – a process known as gene flow . For example, wind or can carry pollen or seeds from one plant population to another. In baboon troops or wolf packs ( Figure ), 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.
::对所有生物来说,突变是基因变异的最终来源。 但是,对于人口来说,个人或网友的移民或移民也可能增加或减少基因库 — — 一个被称为基因流动的过程。 比如,风或者可以把花粉或者种子从一个植物群体带到另一个植物群体。 在浣熊部队或者狼群中(图 ) , 少年男性可能会离开这个群体寻找伴侣,建立不同的人口群体。 人类历史包括无数的移民;基因流动继续混合基因库并导致微变。Dominant alpha wolves lead their pack in Yellowstone National Park. The lowest ranking omega individual, in the rear, may eventually leave the pack to find a mate and establish his own territory and pack. He would carry some of the genes from his pack to the new one – a form of gene flow which seems built into wolves’ social organization.
::在黄石公园,占支配地位的甲型狼领队在黄石公园。 在后方,最底层的欧美加人可能最终离开背包寻找伴侣,建立自己的领地和包包。 他将把一些基因从背包运到新的背包 — — 一种似乎存在于狼社会组织中的基因流动形式。Gene flow can bring new alleles into a population which occurred by chance and were successful in other populations. In this way, it can accelerate microevolution . However, if exchange between populations is frequent, it reduces differences between populations, in effect increasing population size . In this case, gene flow tends to maintain separate populations as one , reducing , if not microevolution.
::基因流动可以给偶然发生并在其他人群中成功的人群带来新的基因源。 这样,基因流动可以加速微进。 但是,如果人口之间的交流频繁,则会缩小人口之间的差异,从而导致人口规模的扩大。 在这种情况下,基因流动倾向于将不同人口维持为一体,即使不是微进,也会减少(如果不是微进的话 ) 。Mutations, together with recombination of existing alleles by , provide the diversity which is the raw material for natural selection and evolution. Gene flow can accelerate the spread of alleles or reduce the differences between populations. Both can contribute significantly to microevolution. However, many biologists consider the major causes of microevolutionary change to be and natural selection.
::基因流动可以加速基因的传播或缩小人口之间的差别,两者都可以大大促进微进。 然而,许多生物学家认为微进变化的主要原因和自然选择是微进变化的主要原因。Summary
::摘要-
Random, spontaneous mutations constantly generate new alleles in a gene pool, destabilizing genetic equilibrium and creating the potential for adaptation to changing environments.
::随机、自发的突变不断在基因库中产生新的异灵,破坏基因平衡的稳定,并创造适应变化环境的潜力。 -
In multicellular organisms, only mutations that affect germ cells become part of the gene pool.
::在多细胞生物中,只有影响细菌细胞的突变才成为基因库的一部分。 -
Because of extensive “junk” DNA, repair enzymes, and multicellularity, many mutations do not reach the gene pool.
::由于大量的“垃圾”DNA、修复酶和多细胞性,许多突变没有到达基因库。 -
Many mutations are harmful, disrupting protein function.
::许多突变是有害的,扰乱蛋白质功能。 -
Because the genetic code is redundant and some amino-acid substitutions may not change protein function, many mutations have no effect on an organism’s fitness.
::因为基因编码是多余的, 某些氨基酸替代物可能不会改变蛋白质功能, 许多突变对生物体的健康状况没有影响。 -
Even neutral mutations hold potential for future selection if the environment changes.
::如果环境发生变化,即使是中性的突变也有可能在今后进行选择。 -
A few mutations may be advantageous, improving or changing protein function.
::一些突变可能有利,改善或改变蛋白质功能。 -
In microorganisms mutation rates are much higher due to rapid reproduction and small genomes.
::在微生物中,由于繁殖迅速和基因组小,突变率要高得多。 -
Mutation, together with recombination of existing alleles provides the diversity which is the raw material for natural selection and evolution.
::变异,加上现有异灵的重新组合,提供了多样性,而多样性是自然选择和演变的原材料。 -
The movement of genes from one population to another (gene flow) can change allele frequencies.
::基因从一个种群向另一个种群的移动(基因流动)可以改变所有基因的频率。 -
Gene flow can accelerate the spread of successful alleles or reduce differences between populations.
::基因流动可以加速成功的灵源的传播或减少人口之间的差别。
Review
::回顾-
Analyze the possible effects of mutations and the probability and importance of each type of mutation.
::分析突变的可能影响和每种变异的概率和重要性。 -
Describe two possible effects of gene flow on the genetics of a population.
::描述基因流动对人口基因的两种可能的影响。
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Random, spontaneous mutations constantly generate new alleles in a gene pool, destabilizing genetic equilibrium and creating the potential for adaptation to changing environments.
