hce_kmu
104年
普通生物及生化概論
第 71 題
The following table compares the % sequence homology of four different parts (two introns and two exons) of a gene that is found in five different eukaryotic species. The data reported for species A were obtained by comparing DNA from one member of species A to another member of species A.
| Species | Intron I | Exon I | Intron VI | Exon V |
|---|---|---|---|---|
| A | 100% | 100% | 100% | 100% |
| B | 99% | 98% | 82% | 96% |
| C | 99% | 98% | 89% | 96% |
| D | 99% | 98% | 92% | 97% |
| E | 99% | 98% | 80% | 94% |
Which of these four gene parts should allow the construction of the most accurate phylogenetic tree, assuming that this is the only part of the gene that has acted as a reliable molecular clock?
| Species | Intron I | Exon I | Intron VI | Exon V |
|---|---|---|---|---|
| A | 100% | 100% | 100% | 100% |
| B | 99% | 98% | 82% | 96% |
| C | 99% | 98% | 89% | 96% |
| D | 99% | 98% | 92% | 97% |
| E | 99% | 98% | 80% | 94% |
Which of these four gene parts should allow the construction of the most accurate phylogenetic tree, assuming that this is the only part of the gene that has acted as a reliable molecular clock?
- A Exon I
- B Exon V
- C Intron I
- D Intron VI
- E Both Exon I and V
思路引導 VIP
如果你想根據幾位同學的賽跑成績來排列名次，而第一組計時數據顯示大家的成績幾乎一模一樣（例如都是 10.0 秒），第二組數據則呈現出明顯的差距（例如從 10.2 秒到 12.5 秒不等），哪一組數據能讓你更精確地排出誰快誰慢？這與表格中各個基因片段提供的百分比分布有什麼相似之處呢？
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AI 詳解
AI 專屬家教
太棒了！你能精準選出 (D) Intron VI，代表你對「分子鐘」的概念以及數據分析的敏銳度非常優秀。這道題目考察的關鍵在於如何從序列同源性（Homology）中找出足以區分物種的「解析度」。
分子鐘的解析度與演化資訊
要建構一棵準確的親緣關係樹，我們需要尋找具有適度變異率的遺傳標記。在表格中，Intron I、Exon I 與 Exon V 在不同物種間的數值非常接近（多介於 94% 至 99%），這意味著這些序列演化過於緩慢，提供的資訊不足以分辨物種間的細微差異。而 Intron VI 的數值分布最廣（80% 至 92%），這種明顯的梯度變化能讓我們更清晰地判斷誰與 A 物種親緣關係較近，誰又較遠，就像是一把刻度更精細的尺。
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