hce_nthu
115年
生物與生化
第 48 題
A specific locus in a large, sexually reproducing deer mouse population is analyzed. Researchers find that the locus exhibits high nucleotide variability (many base-pair differences across individuals) but extremely low gene variability (less than 1% heterozygosity). Assuming this population is large and mating is random, which explanation best accounts for the coexistence of these two variability measurements?
- A The high nucleotide variability is solely maintained by directional selection favoring one homozygous genotype.
- B Genetic drift has caused the rapid fixation of the most common allele, simultaneously eliminating all new nucleotide mutations.
- C The majority of the nucleotide differences occur in noncoding regions (introns) or represent silent substitutions, resulting in few distinct functional alleles (low gene variability).
- D Balancing selection is actively maintaining two or more forms in the population, contradicting the observed low heterozygosity.
- E Gene flow is consistently introducing new alleles that are immediately selected against before they can be replicated within the population.
思路引導 VIP
想像一段極長的遺傳密碼中，只有極小比例的部分會真正決定蛋白質的構造與功能。如果今天發生了大量的序列變動，卻完全沒有影響到生物的生存表現或等位基因的類型，你覺得這些變動最可能隱藏在基因組的哪些「不被看見」的區域，或是以什麼樣的形式存在，才不會改變最終產物的結果呢？
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AI 詳解
AI 專屬家教
分子多樣性與功能的解構
太棒了！你能精準辨析「核苷酸變異度」與「基因變異度」這兩個容易混淆的概念，這代表你對現代演化生物學的分子基礎掌握得非常紮實。這題的正確答案為 (C)，主要原因在於基因組中並非所有序列都會影響性狀。在一個大型且隨機交配的族群中，雖然 DNA 序列在微觀層面可能累積了大量的鹼基替換，但如果這些變異大多落在內含子（Introns）等非編碼區，或是屬於不改變氨基酸序列的沈默突變（Silent mutations），那麼在功能層面上就不會產生新的等位基因（Alleles），進而導致觀察到的異型合子頻率（Heterozygosity）極低。
中性演化與鑑別度點評
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