Molecular Comparisons between Species | 物种间的分子比较

📚 Molecular Comparisons between Species | 物种间的分子比较

Molecular comparisons provide powerful evidence for evolutionary relationships by examining similarities and differences in DNA, RNA and proteins. Unlike morphological traits, molecules accumulate changes in a more predictable way, allowing biologists to estimate how closely related two species are and when they shared a common ancestor.

分子比较通过检查 DNA、RNA 和蛋白质的相似性与差异，为进化关系提供了有力证据。与形态特征不同，分子以更可预测的方式积累变化，使生物学家能够估计两个物种的亲缘关系远近以及它们何时共享共同祖先。

1. Why Molecular Comparisons Matter | 为什么分子比较很重要

Molecular comparisons provide a more direct window into evolutionary history than many morphological features. Because DNA sequences are inherited and change over generations, shared sequences imply common ancestry, while differences accumulate after lineages separate.

分子比较比许多形态特征更直接地反映了进化历史。由于 DNA 序列可以遗传并随世代发生变化，共有序列意味着共同祖先，而差异则是在谱系分开后积累的。

In addition, molecules are universal: all living organisms use DNA, RNA and proteins, so the same genes can be compared across bacteria, fungi, plants and animals. This universality makes molecular data especially valuable for building large-scale phylogenies.

此外，分子具有普遍性：所有生物都使用 DNA、RNA 和蛋白质，因此可以在细菌、真菌、植物和动物之间比较相同的基因。这种普遍性使分子数据对于构建大规模系统发育树特别有价值。

2. DNA Hybridisation | DNA 杂交

DNA hybridisation was one of the first molecular techniques used to compare whole genomes without sequencing them. Double-stranded DNA from two species is denatured by heating, then mixed and cooled. The rate of re-association and the thermal stability of the hybrid double helix indicate how similar the base sequences are.

DNA 杂交是最早用于在不测序的情况下比较整个基因组的分子技术之一。将来自两个物种的双链 DNA 加热变性，然后混合并冷却。重新结合的速率以及杂交双螺旋的热稳定性表明碱基序列的相似程度。

A lower hybridisation temperature or a lower melting temperature (Tₘ) means fewer hydrogen bonds formed between the two strands, so the species are less closely related. Conversely, closely related species have hybrids that remain stable at higher temperatures.

较低的杂交温度或较低的熔解温度 (Tₘ) 意味着两条链之间形成的氢键较少，因此物种的亲缘关系较远。相反，亲缘关系近的物种产生的杂交体在较高温度下仍能保持稳定。

3. DNA Sequencing | DNA 测序

DNA sequencing provides the ultimate resolution because it determines the exact order of nucleotides. In modern studies, homologous genes or whole genomes are aligned using software, and positions that differ are counted to produce a measure of genetic distance.

DNA 测序提供了最高的分辨率，因为它确定了核苷酸的精确顺序。在现代研究中，同源基因或整个基因组通过软件进行比对，统计不同的位置以产生遗传距离的度量。

For example, the COI gene (cytochrome c oxidase subunit I) is used as a barcode in animals. If two specimens have a

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