Diversity, classification and a branching model
הוצג| English | משמעות |
|---|---|
| taxon/ˈtæksn/ | טקסון |
| clade/kleɪd/ | קלייד |
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.
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?
רמת קושי 1/5 · 100 מטבעות + בונוס קטן בהשלמה הראשונה היום
Rotating branches at a node changes only the drawing order; the branching pattern - which groups share which ancestors - is untouched. Tip order on the page is not a sequence of progress or time.
Match each technical term to its precise meaning.
רמת קושי 2/5 · 140 מטבעות + בונוס קטן בהשלמה הראשונה היום
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.
In the lab: 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?
רמת קושי 2/5 · 140 מטבעות + בונוס קטן בהשלמה הראשונה היום
Stating the conditions and assumptions lets others repeat the work exactly, and recording the supporting evidence lets them check the conclusion. Hiding disagreeing results removes the evidence that could challenge a wrong conclusion, and one measurement can never establish a wider claim.
Work from known quantities
- 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.
Your turn: There are 8 differences in 50 aligned sites. Calculate percentage difference.
There are 8 differences in 50 aligned sites. Calculate percentage difference.
רמת קושי 2/5 · 140 מטבעות + בונוס קטן בהשלמה הראשונה היום
The result is 16 %. Known: 8 differences in 50 aligned sites. Use percentage difference = differences / sites x 100. Difference = 8/50 x 100 = 16%. This observed percentage is not a molecular-clock estimate without rate assumptions.
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.
Not true: Every cladogram branch length is a measurement of elapsed time. Branch lengths mean time only in trees explicitly drawn with a time or change scale. Many cladograms encode relationships only, with arbitrary lengths.
- A species is a biological grouping; a taxon is a named classification group.
- Read relationships from the branching order.
- Watch for: A modern species is not automatically the ancestor of another modern species.
Write from a difference of 28 percent
- An alignment has 7 differences in 25 sites.
- Find the percentage difference. Say what rotating a branch does.
Branch lengths mean time only in trees explicitly drawn with a time or change scale.
רמת קושי 1/5 · 100 מטבעות + בונוס קטן בהשלמה הראשונה היום
True. Branch lengths mean time only in trees explicitly drawn with a time or change scale. Many cladograms encode relationships only, with arbitrary lengths.
A named group in a classification: write the technical term.
רמת קושי 1/5 · 100 מטבעות + בונוס קטן בהשלמה הראשונה היום
taxon means A named group in a classification.
An alignment has 7 differences in 25 sites. What is the percentage difference, and does rotating branches at a node change the ancestry?
7 out of 25 is 28 percent. The branching order, not the left-right drawing, shows ancestry.
What is the percentage difference?
רמת קושי 1/5 · 100 מטבעות + בונוס קטן בהשלמה הראשונה היום
7 divided by 25 is 0.28, which is 28 percent.