hce_kmu
105年
普通生物及生化概論
第 70 題
As discussed in the text, the fruit fly Drosophila melanogaster has an allele that confers resistance to DDT and similar insecticides. Laboratory strains of D. melanogaster have been established from flies collected in the wild in the 1930s (before the widespread use of insecticides) and the 1960s (after 20 years of DDT use). Lab strains established in the 1930s have no alleles for DDT resistance. In lab strains established in the 1960s, the frequency of the DDT-resistance allele is 37%. Which statement below is true?
- A Some fruit flies evolved resistance to DDT in order to survive.
- B The heritable trait of DDT resistance cannot change even DDT use became widespread.
- C Fruit flies became more resistant to DDT over time.
- D When DDT was widely used, fruit flies with DDT resistance had greater evolutionary fitness than fruit flies lacking DDT resistance.
- E Alleles for DDT resistance arose by mutation during the period of DDT use because of selection for pesticide resistance.
思路引導 VIP
如果我們觀察到一個族群中某個特徵的比例在短時間內大幅增加，這通常代表擁有該特徵的個體在當時的環境下，比起其他個體在「生存」與「傳承後代」這兩件事上具備什麼樣的優勢？這種優勢與環境變化之間存在著什麼樣的關係呢？
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AI 詳解
AI 專屬家教
同學太棒了！你能精確判斷出 (D) 這個選項，代表你對於「自然選擇」（Natural Selection）的核心概念有著非常紮實且正確的理解。這道題目給出的實驗數據是演化生物學中的經典案例，而你成功避開了常見的直覺陷阱。
自然選擇與相對適應值
這題的核心在於理解環境如何篩選基因頻率。在 1930 年代 DDT 尚未普及時，抗藥性基因對果蠅可能沒有額外好處甚至是有害的；但到了 1960 年代，環境中充滿了殺蟲劑，這時擁有抗藥性等位基因（Allele）的個體，其生存並留下後代的機率大幅提升，這就是所謂的 適應值（Fitness） 較高。因此，該基因在族群中的頻率才會從趨近於零上升至 37%。
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