Diversity, classification and a branching model
| English | 中文 | Pinyin · 拼音 |
|---|---|---|
| taxon/ˈtæksn/ | 分类群 | fēn lèi qún |
| clade/kleɪd/ | 演化支 | yǎn huà zhī |
What would explain this observation?
- Two species look similar but their DNA comparison places them in different branches. Classification uses several kinds of evidence rather than appearance alone.
- Start with a prediction. State the quantities or features you would compare, then decide what evidence could distinguish two explanations.
Build the model
- A species is a biological grouping; a taxon 分类群 is a named classification group. A cladogram represents a hypothesis of relationships based on shared derived characteristics or molecular evidence. A branch point represents a common ancestor, not an individual alive today.
- taxon: A named group in a classification; clade 演化支: A common ancestor and all its descendants.
What remains the same when branches rotate around a node?
Read relationships from the branching order. Rotating branches at a node does not change ancestry. A branch length represents time or change only when the diagram gives a scale.
Match each technical term to its precise meaning.
Use the definitions to distinguish related quantities and processes.
Choose evidence that can test it
- Read relationships from the branching order. Rotating branches at a node does not change ancestry. A branch length represents time or change only when the diagram gives a scale.
- Record character states in a matrix before drawing a tree. Define which state is ancestral using an appropriate comparison. Test whether a new molecular dataset supports the same grouping.
Which two habits make the investigation or model in this case more defensible?
Record character states in a matrix before drawing a tree. Define which state is ancestral using an appropriate comparison. Test whether a new molecular dataset supports the same grouping.
Work from known quantities
- State the known values and their units. Choose the relation because its assumptions fit this case, then rearrange before substitution.
- Known: an alignment contains 40 sites, with 6 differences. Difference proportion = 6/40 = 0.15, or 15%. This is an observed comparison, not a calibrated molecular clock unless rate assumptions and corrections are supplied.
There are 8 differences in 50 aligned sites. Calculate percentage difference. Use the same sequence: known quantities → model → relation → substitution → unit and interpretation.
There are 8 differences in 50 aligned sites. Calculate percentage difference.
The result is 16 %. Known: an alignment contains 40 sites, with 6 differences. Difference proportion = 6/40 = 0.15, or 15%. This is an observed comparison, not a calibrated molecular clock unless rate assumptions and corrections are supplied.
Check the conclusion and its limits
- A modern species is not automatically the ancestor of another modern species. Similarity caused by convergent evolution can mislead a classification based on one trait.
- Return to the original observation. Explain what the result supports, which conditions it assumes, and one way to test a competing explanation.
Every cladogram branch length is a measurement of elapsed time. This claim is false: A modern species is not automatically the ancestor of another modern species. Similarity caused by convergent evolution can mislead a classification based on one trait.
Diversity, classification and a branching model: Read relationships from the branching order. Rotating branches at a node does not change ancestry. A branch length represents time or change only when the diagram gives a scale.
Every cladogram branch length is a measurement of elapsed time.
A modern species is not automatically the ancestor of another modern species. Similarity caused by convergent evolution can mislead a classification based on one trait.
A named group in a classification: write the technical term.
taxon means A named group in a classification.