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IB Biology > 5.4 Cladistics > Flashcards

5.4 Cladistics Flashcards

(46 cards)

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1
Q

What is cladistics?

A

Cladistics is a method of classifying organisms into groups of species called clades

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2
Q

What does each clade consist of?

A

An ancestral organism and all of its evolutionary descendants

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3
Q

What will members of a clade possess?

A

Common characteristics as a result of their shared evolutionary lineage

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4
Q

What are cladograms?

A

They are tree diagrams where each branch point represents the splitting of two new groups from a common ancestor

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5
Q

What is a branch point also called?

A

Node

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6
Q

What does each node represent?

A

A speciation event by which distinct species are formed via divergent evolution

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7
Q

What do cladograms show?

A

Cladograms show the probable sequence of divergence, the likely evolutionary relationships and how recently they showed a common ancestor

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8
Q

The fewer the number of nodes between two groups…

A

The more closely related they are expected to be

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9
Q

What clade do humans, chimpanzees, gorillas, orangutans and gibbons all belong to?

A

The hominoids

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10
Q

What does the hominoid clade belong to?

A

A larger clade called the anthropoids

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11
Q

What are the four key features of a cladogram?

A

Root
Nodes
Outgroup
Clades

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12
Q

What is a root?

A

The initial ancestor common to all organisms within the cladogram

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13
Q

What is a node?

A

Each node corresponds to a hypothetical ancestor that speciated to give rise to two or more daughter taxa

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14
Q

What is an outgroup?

A

The most distantly related species in the cladogram which functions as a point of comparison and reference group

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15
Q

What are clades?

A

A common ancestor and all of its descendants

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16
Q

What can cladograms be constructed based on?

A

Structural evidence or molecular evidence

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17
Q

What is the preferred evidence used when constructing cladograms?

A

Molecular evidence

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18
Q

What are the steps to constructing a cladogram based on structural evidence?

A
  1. Organise selected organisms according to defined characteristics
  2. Sequentially order organisms according to shared characteristics to construct a cladogram
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19
Q

What are the steps to constructing a cladogram based on molecular evidence?

Study These Flashcards
A
  1. Select a gene or protein common to a range of selected organisms
  2. Copy the molecular sequence for each of the selected organisms
  3. Run a multiple alignment to compare molecular sequences
  4. Generate a cladogram from multiple alignment data
20
Q

What does a shared molecular heritage mean?

Study These Flashcards
A

Base and amino acid sequences can be compared to ascertain levels of relatedness

21
Q

What do all organisms use DNA and RNA for?

Study These Flashcards
A

Genetic material

22
Q

What demonstrates the degree of evolutionary divergence?

Study These Flashcards
A

The number of differences between comparable base sequences

23
Q

What does a greater number of differences between comparable base sequences suggest?

Study These Flashcards
A

More time has passed since two species diverged

24
Q

The more similar the base sequence of two species are…

Study These Flashcards
A

The more closely related the two species are

25
What do scientists use when comparing molecular sequences?
Non coding DNA Gene sequences Amino acid sequences
26
Tell me about non coding DNA when comparing molecular structures?
Non coding DNA is the best for comparison as mutations will occur more often in the sequences
27
Tell me about gene sequences when comparing molecular structures?
Gene sequences mutate at a slower rate as changes in base sequences may affect protein structure and function
28
Tell me about amino acid sequences when comparing molecular structures?
Whilst amino acid sequences are used for comparison they have the slowest mutation rate due to codon degeneracy
29
What are amino acid sequences typically used to compare?
Distantly related species
30
What are DNA and RNA base sequences typically used to compare?
Closely related organisms
31
What is there a positive correlation between?
The number of differences between two species and the time since they diverged from a common ancestor
32
If the rate of change is reliable what can scientists calculate?
Scientists can calculate the time of divergence according to the number of differences
33
What is the molecular clock?
How scientists can calculate the time of divergence according to the number of differences using the reliable rate of change of mutations
34
What are factors that limit the molecular clock?
- different genes and proteins change at different rates - The rate of change for a particular gene may differ between different groups of organisms - Earlier changes may be reversed by later changes potentially impacting the accuracy of predictions
35
What was classification historically based on?
Structural characteristics
36
What were closely related species expected to show?
Similar structural features
37
What are the two limitations of using structural differences for classification?
Closely related organisms can show different structural features due to adaptive radiation Distantly related organisms can show similar features due to convergent evolution
38
What is convergent evolution?
Convergent evolution is the independent evolution of similar features in species with distinct lineages
39
When may convergent evolution occur?
When different species have the same habitat and have the same selection pressures
40
What does shared conditions cause?
Common adaptations in different species causing similar structural features
41
What are homologous structures?
Traits that are similar because of common ancestry
42
What are analogous structures?
Traits that are superficially similar due to common selection pressures but happen through separate evolutionary pathways
43
What has molecular evidence helped scientists show?
That species once thought to be closely related due to similar structural features actually showed very different evolutionary origins
44
Why were figworts problematic?
Many of the figwort plants had too different structures to function as a meaningful grouping
45
What did the taxonomists examine to split the figwort species into smaller clades?
The chloroplast gene
46
What size were figworts before and after reclassification?
8th largest to 36th largest

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