| Core | Supplement |
|---|---|
| 1 Describe variation as differences between individuals of the same species | |
| 2 State that continuous variation results in a range of phenotypes between two extremes; examples include body length and body mass | |
| 3 State that discontinuous variation results in a limited number of phenotypes with no intermediates; examples include ABO blood groups, seed shape in peas and seed colour in peas | |
| 4 State that discontinuous variation is usually caused by genes only and continuous variation is caused by both genes and the environment | |
| 5 Investigate and describe examples of continuous and discontinuous variation | |
| 6 Describe mutation as genetic change | 9 Describe gene mutation as a random change in the base sequence of DNA |
| 7 State that mutation is the way in which new alleles are formed | 10 State that mutation, meiosis, random mating and random fertilisation are sources of genetic variation in populations |
| 8 State that ionising radiation and some chemicals increase the rate of mutation |
变异与选择
IGCSE 生物 · 第 18 主题
18.1
变异
大纲
来源:剑桥国际大纲
变异(variation)意味着同一物种(species)个体之间的差异。有两种类型:
- 连续变异(continuous variation)——两个极端之间表现型(phenotypes)的一个平滑范围(例如身长和体重)。
- 不连续变异(discontinuous variation)——几个分开的表现型,中间什么都没有(例如 ABO 血型(ABO blood groups),或豌豆的种子形状)。
不连续变异通常只由基因(genes)引起。连续变异由基因和环境(environment)两者引起——例如,你的身高取决于你的基因,也取决于你的饮食。
Mutation
一个突变(mutation)是一个遗传改变。突变是新****等位基因(alleles)被制造的方式,所以它们是所有变异的原始来源。(补充) 一个基因突变(gene mutation)是 DNA 的碱基序列(base sequence)中的一个随机改变。
电离辐射(ionising radiation,如 X 射线)和一些化学物提高突变的速率(rate)。(补充) 遗传变异的其他来源是减数分裂(meiosis)、随机交配和随机受精(fertilisation)。
探索
Variation lab
Classify examples of variation by pattern and cause.
词汇表
训练
| 英文 | 中文 | 拼音 |
|---|---|---|
| variation | 变异 | biàn yì |
| species | 物种 | wù zhǒng |
| continuous variation | 连续变异 | lián xù biàn yì |
| phenotypes | 表现型 | biǎo xiàn xíng |
| discontinuous variation | 不连续变异 | bù lián xù biàn yì |
| ABO blood groups | 血型 | xuè xíng |
| genes | 基因 | jī yīn |
| environment | 环境 | huán jìng |
| mutation | 突变 | tū biàn |
| alleles | 等位基因 | děng wèi jī yīn |
| gene mutation | 基因突变 | jī yīn tū biàn |
| base sequence | 碱基序列 | jiǎn jī xù liè |
| ionising radiation | 电离辐射 | diàn lí fú shè |
| rate | 速率 | sù lǜ |
| meiosis | 减数分裂 | jiǎn shù fēn liè |
| fertilisation | 受精 | shòu jīng |
18.2
适应性特征
大纲
| Core | Supplement |
|---|---|
| 1 Describe an adaptive feature as an inherited feature that helps an organism to survive and reproduce in its environment | |
| 2 Interpret images or other information about a species to describe its adaptive features | |
| 3 Explain the adaptive features of hydrophytes and xerophytes to their environments |
来源:剑桥国际大纲
一个适应特征(adaptive feature)是一个帮助一个生物体在它环境中生存(survive)和生殖(reproduce)的遗传(inherited)特征。
(补充)
- 水生植物(hydrophytes,水生植物)有像气腔的特征以帮助它们浮起,以及叶上表面的气孔。
- 旱生植物(xerophytes,沙漠植物)有像厚蜡质角质层、少而小的气孔,以及储存水的能力的特征——都是为了减少水分流失。
探索
Selection shapes adaptations
On a dark, sooty tree the better-camouflaged moths survive and breed, so the population shifts — adaptive features arise by natural selection.
词汇表
训练
| 英文 | 中文 | 拼音 |
|---|---|---|
| adaptive feature | 适应特征 | shì yìng tè zhēng |
| inherited | 遗传 | yí chuán |
| survive | 生存 | shēng cún |
| reproduce | 生殖 | shēng zhí |
| hydrophytes | 水生植物 | shuǐ shēng zhí wù |
| xerophytes | 旱生植物 | hàn shēng zhí wù |
18.3
选择
大纲
| Core | Supplement |
|---|---|
| 1 Describe natural selection with reference to: (a) genetic variation within populations (b) production of many offspring (c) struggle for survival, including competition for resources (d) a greater chance of reproduction by individuals that are better adapted to the environment than others (e) these individuals pass on their alleles to the next generation | 4 Describe adaptation as the process, resulting from natural selection, by which populations become more suited to their environment over many generations |
| 5 Describe the development of strains of antibiotic resistant bacteria as an example of natural selection | |
| 2 Describe selective breeding with reference to: (a) selection by humans of individuals with desirable features (b) crossing these individuals to produce the next generation (c) selection of offspring showing the desirable features | |
| 3 Outline how selective breeding by artificial selection is carried out over many generations to improve crop plants and domesticated animals and apply this to given contexts | 6 Outline the differences between natural and artificial selection |
来源:剑桥国际大纲
自然选择(natural selection)解释一个物种如何变得更适合它的环境:
- 一个种群中有遗传变异(由突变引起)。
- 生物体产生许多后代(offspring)——多于能存活的。
- 有一个生存斗争,为食物和空间等资源(resources)竞争(competition)。
- 更好适应(adapted)的个体更可能存活和生殖。
- 它们传递它们的等位基因,所以有益的等位基因在下一代变得更常见。
(补充) 经过许多代这使种群更适合它的环境;这个过程叫适应。一个清晰的例子是抗生素(antibiotic)耐药细菌(bacteria):少数细菌携带一个耐药(resistant)等位基因并在抗生素中存活,然后繁殖,直到整个种群耐药。
例题。 某种蛾大多是浅色的。煤烟把它们停歇的树干熏黑,几十年内大多数蛾都变成了深色。请用自然选择解释。变异本来就存在:偶然地有少数深色蛾,由突变引起。在被熏黑的树皮上,深色蛾伪装得更好,所以鸟吃掉的更少,它们更可能存活。存活者繁殖,把深色的等位基因传给后代,所以它每一代都变得更常见,直到大多数蛾都是深色。按这条链来写:变异、存活、繁殖、等位基因变得更常见。蛾不是为了躲藏才变黑的 - 只是深色的那些存活得更多。
探索
Natural selection
Individuals best suited to their environment survive and pass on their genes — so the population changes over time.
探索
Natural selection
Run the generations: birds eat the moths that stand out, so the camouflaged ones survive and breed — the population shifts to match the forest.
词汇表
训练
| 英文 | 中文 | 拼音 |
|---|---|---|
| natural selection | 自然选择 | zì rán xuǎn zé |
| many offspring | 后代 | hòu dài |
| competition | 竞争 | jìng zhēng |
| resources | 资源 | zī yuán |
| adapted | 适应 | shì yìng |
| antibiotic | 抗生素 | kàng shēng sù |
| bacteria | 细菌 | xì jūn |
| resistant | 耐药 | nài yào |
18.3
选择育种
在选择育种(selective breeding,也叫人工选择(artificial selection))中,人类选择哪些生物体繁殖:
- 选择有你想要特征的个体。
- 把它们杂交以产生下一代。
- 选择显示那些特征的后代,并经过许多代重复。
这被用来改良农作物(crops,例如一个更高的产量)和农场动物(例如给更多奶的奶牛)。
(补充) 关键的区别:在自然选择中环境决定哪些个体存活;在人工选择中人类决定。
探索
Selective breeding
Humans choose which organisms breed, to develop a useful feature over many generations.
词汇表
训练
| 英文 | 中文 | 拼音 |
|---|---|---|
| selective breeding | 选择育种 | xuǎn zé yù zhǒng |
| artificial selection | 人工选择 | rén gōng xuǎn zé |
| crops | 农作物 | nóng zuò wù |
18.3
考试技巧
- 连续变异 = 一个范围(基因 + 环境);不连续 = 分开的组(只有基因)。
- 突变制造新等位基因——所有变异的来源。辐射和一些化学物提高突变速率。
- 自然选择:变异 → 太多的后代 → 斗争和竞争 → 最好适应的存活和生殖 → 它们传递它们的等位基因。
- 细菌中的抗生素耐药性是自然选择在行动。
- 选择育种(人工选择):人类挑选亲代;在自然选择中,环境"挑选"。
本主题的互动课程
逐步学习,并即时检测练习。