IB Biology: 5.4
Terms in this set (23)
A group of organisms consisting of a common ancestor and all of its descendants
A method of classifying living organisms based on the construction and analysis of cladograms.
Tree diagrams that show the most probable sequence of divergence in clades.
Each node corresponds to a hypothetical common ancestor that speciated to give rise to two (or more) daughter taxa
The initial ancestor common to all organisms within the cladogram
The most distantly related species in the cladogram which functions as a point of comparison and reference group
Analysis of cladograms
- More nodes between two species, the less related they are expected to be.
- The sequence of splits at nodes indicates when species diverged.
Cladogram of some primates
How to deduce if species evolved from a common ancestor
(1) Base sequences of genes or amino acid sequences are used
(2) Species with a recent common ancestor will have fewer differences
(3) Species with an ancient common ancestor (10s of mya) have many
Why is there a positive correlation between the number of differences between two species and the time since they diverged from a common ancestor?
since base sequences accumulate (gather together) gradually.
The average rate that a species' genome mutates. This calculates when evolutionary divergence occurred from the common ancestor
Similar structures due to similar ancestry; Arise via divergent evolution; E.g. Pentadactyl Limb
-> the opposite of homologous structures. Similar structures due to convergent evolution (similar functionality). E.g. Fins of shark and whale
Deducing common ancestors using form and structure. This is inaccurate because it can be tough to distinguish homologous and analogous structures
Why reclassification is important in cladistics
This pushes classes closer to natural classification, revealing unnoticed similarities between groups. The predictive value is, therefore, higher.
- A natural classification should be based on homologous characteristics.
-Analogous characteristics can cause confusion and muddle the true classification.
the regrouping of species as more evidence becomes available as to their evolutionary origins.
- Resulted from the analysis of DNA base and amino acid sequences allowed biochemical cladograms.
Closest relatives to humans
Chimpanzees and bonobos
When the closest relatives to humans evolved
According to a molecular clock with a mutation rate of 10^-9 yr^-1:
Humans branched off 4.5 myr.
Chimpanzees branched off 1 myr.
Early massive family in cladistics organized by morphology. It had over 5 000 species
What was found about the figwort family
It was not a true clade; five clades had been initially combined into one family.
Why cladograms are not always accurate
They assume the smallest possible number of mutations occurred, which may be wrong.
evidence from cladistics has shown that classifications of some groups based on structure did not correspond with the evolutionary origins of a group or species.
Divergent Evolution (adaptive radiation)
the rapid evolutionary diversification of a single ancestral line
It occurs when members of a single species occupy a variety of distinct niches with different environmental conditions
The independent evolution of similar features in species with distinct lineages
Occurs when different species occupy the same habitat and are subjected to the same environmental pressures (e.g. wings in birds and bats)
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