选择性育种
爱德思国际普通中等教育证书（IGCSE）生物· 5.10–5.11（2017年第3版大纲）· 12 分钟阅读
1. 选择性育种的流程★★☆☆☆⏱ 3 min
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选择性育种（人工选择）
人类有意选择具备优良性状的生物进行交配繁殖，经过多代培育，产出能够稳定表达这些目标优良性状的后代的过程。
Select parent organisms that show the desired characteristic
Breed the selected parents together
Select the offspring that show the strongest expression of the desired characteristic
Breed these selected offspring together
Repeat the selection and breeding cycle over many generations until all offspring reliably show the desired trait
某农民想要培育出谷物产量更高的小麦植株，请简述他使用选择性育种的操作流程。
- 1
- 首先，农民从他的现有作物中挑选出谷物产量最高的小麦植株。
- 2
- 他将这些高产的亲代小麦植株进行杂交，让它们完成授粉并结出种子。
- 3
- 他将这些种子培育为新的小麦植株，之后挑选出谷物产量最高的子代植株。
- 4
- 他将这些高产子代植株进行杂交，重复选择和育种循环多代。
- 5
- 经过多代之后，培育出的所有小麦植株都将稳定拥有远高于原始作物的谷物产量。
Exam tip:
答题时务必提及多代重复循环：这几乎是所有选择性育种流程类考题的必拿分要点。
2. 植物的选择性育种★★☆☆☆⏱ 3 min
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选择性育种在农业中被广泛用于改良粮食生产类作物，筛选出的性状可以提升产量、降低病害损失，或是提升对消费者的吸引力。
Higher yield grain crops (wheat, rice, maize)
Disease-resistant fruit and vegetable crops
Drought-resistant crops for dry growing regions
Ornamental flowers with larger, more colourful blooms for horticulture
某园艺师想要培育出能开出深红色、香气浓郁花朵的玫瑰植株，请描述选择性育种实现该目标的过程。
- 1
- 从现有种群中挑选出花朵颜色最深红、香气最浓郁的亲代玫瑰植株。
- 2
- 对这些挑选出的亲代玫瑰进行异花授粉，结出种子。
- 3
- 将种子培育为新的玫瑰植株，筛选出同时拥有深红色花朵和浓郁香气的子代植株。
- 4
- 将这些筛选出的子代植株进行杂交，重复该循环多代，直到所有子代都能稳定开出深红色、香气浓郁的花朵。
Exam tip:
回答植物选择性育种相关考题时，请使用广泛公认的农业/园艺领域实例，这类实例在评分标准中有明确列出。
3. 动物的选择性育种★★☆☆☆⏱ 3 min
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选择性育种被应用于家畜、伴侣动物和工作用动物的培育，筛选出对人类有用或能够提升动物福利的性状。
Dairy cattle with high milk yield
Beef cattle with high meat yield
Sheep that produce high quality/quantity of wool
Hens that lay large numbers of eggs
Dogs bred for calm temperament (pets) or working ability (sheepdogs, guide dogs)
某牧场主想要提升他饲养的奶牛的产奶量，请解释他如何使用选择性育种实现该目标。
- 1
- 找出他牛群中产奶量最高的奶牛，挑选一头高产的种公牛与这些奶牛交配。
- 2
- 将挑选出的高产奶牛和种公牛进行交配，产下小牛后代。
- 3
- 当雌性幼牛发育成熟后，挑选产奶量最高的个体与另一头高产公牛进行配种。
- 4
- 重复该选育周期多代，直至牛群中的所有奶牛都能稳定产出极高产量的牛奶。
4. 缺点与核心对比★★★☆☆⏱ 3 min
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尽管选择育种能为食品生产和其他领域带来诸多益处，但它也存在考试要求掌握的重要缺陷，同时它与基因工程（另一常与它放在考题中对比的独立知识点）存在核心差异。
基因库
同一物种的种群中存在的全部不同等位基因的总和。
选择育种的一个核心缺点是它会缩小选育种群的基因库规模，因为每一代仅会选育少数带有目标性状的亲本个体，这会降低遗传多样性。这会导致种群被新疾病灭绝的风险升高，同时近缘个体近亲繁殖带来的遗传缺陷发生率也会上升。
Feature | Selective Breeding | Genetic Engineering |
|---|---|---|
Mechanism | Uses natural sexual reproduction, selects for existing variation in the species | Directly transfers specific genes from one organism to another, can cross species barriers |
Speed | Slow, takes many generations to produce desired traits | Fast, traits can be added in a single generation |
Inheritance risk | Higher risk of inherited defects due to inbreeding | Lower risk from inbreeding, though other safety risks apply |
Exam tip:
选择育种和基因工程的对比是分值为3-4分的常见考题：请学习下方表格，确保这类题目拿到满分。
5. 常见陷阱
错误做法:
Only describing 1 or 2 generations of selection
原因:
Mark schemes explicitly require stating the process is repeated over many generations to get full marks.
正确做法:
Always mention that the selection and breeding cycle is repeated over many generations until the trait is reliably expressed in all offspring.
错误做法:
Confusing selective breeding with genetic engineering
原因:
The two processes are often compared in exam questions, and mixing them up leads to lost marks.
正确做法:
Remember selective breeding uses natural reproduction and existing variation, while genetic engineering directly transfers genes between organisms.
错误做法:
Forgetting to mention selection of both parents and offspring
原因:
Both steps are required in the process, missing one loses a mark.
正确做法:
Include selecting parents with the desired trait, then selecting the best offspring to breed in every cycle.
错误做法:
Stating that selective breeding creates new traits
原因:
Selective breeding only selects for existing variation in a population, it does not create new alleles.
正确做法:
State that selective breeding amplifies existing desired traits that are already present in the species.
错误做法:
Not linking reduced genetic variation to increased disease risk
原因:
This is a standard disadvantage asked for in many questions, and requires a causal link to get full marks.
正确做法:
Explain that a smaller gene pool means fewer individuals will have alleles that confer resistance to new diseases, so the population is at higher risk of being wiped out.
6. 速查表
Category | Key Exam Points |
|---|---|
Process Steps |
|
Plant Examples | High yield crops, disease-resistant crops, ornamental flowers |
Animal Examples | High milk yield cattle, high wool yield sheep, high egg-laying hens, calm temperament dogs |
Disadvantages | Reduced gene pool, lower genetic variation, higher risk of disease/inherited defects |
Vs Genetic Engineering | Slow, natural reproduction, no cross-species gene transfer |
7. 常见问题
需要多少代选择才能拿到该考点的满分？
评分标准明确要求你说明选择和育种循环需要重复多代（而非1或2代），直到目标性状在所有后代中稳定表达。遗漏该要点将扣除相应分数。
选择性育种和自然选择的区别是什么？
选择性育种由人类控制，目的是筛选对人类有用的性状；而自然选择由环境压力驱动，筛选能够提升生物生存和繁殖概率的性状。此外，在培育出性状统一的种群方面，选择性育种的速度远快于自然选择。
深入阅读
下一步
Now that you have mastered selective breeding for Edexcel IGCSE Biology, you can move on to the related topics in the biological resources unit. The next core topic is genetic engineering, which is often compared to selective breeding in exam questions, so understanding the differences between the two processes will help you score high marks on comparison questions. You can also review variation and natural selection to consolidate your understanding of how traits are passed between generations, which underpins all selective breeding processes. Make sure to practice past paper questions on selective breeding to apply your knowledge to exam-style scenarios.