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IB Biology > 5.4 Cladistics > Flashcards

5.4 Cladistics Flashcards

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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?

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?

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?

A

Genetic material

22
Q

What demonstrates the degree of evolutionary divergence?

A

The number of differences between comparable base sequences

23
Q

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

A

More time has passed since two species diverged

24
Q

The more similar the base sequence of two species are…

A

The more closely related the two species are

25
Q

What do scientists use when comparing molecular sequences?

A

Non coding DNA
Gene sequences
Amino acid sequences

26
Q

Tell me about non coding DNA when comparing molecular structures?

A

Non coding DNA is the best for comparison as mutations will occur more often in the sequences

27
Q

Tell me about gene sequences when comparing molecular structures?

A

Gene sequences mutate at a slower rate as changes in base sequences may affect protein structure and function

28
Q

Tell me about amino acid sequences when comparing molecular structures?

A

Whilst amino acid sequences are used for comparison they have the slowest mutation rate due to codon degeneracy

29
Q

What are amino acid sequences typically used to compare?

A

Distantly related species

30
Q

What are DNA and RNA base sequences typically used to compare?

A

Closely related organisms

31
Q

What is there a positive correlation between?

A

The number of differences between two species and the time since they diverged from a common ancestor

32
Q

If the rate of change is reliable what can scientists calculate?

A

Scientists can calculate the time of divergence according to the number of differences

33
Q

What is the molecular clock?

A

How scientists can calculate the time of divergence according to the number of differences using the reliable rate of change of mutations

34
Q

What are factors that limit the molecular clock?

A
  • 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
Q

What was classification historically based on?

A

Structural characteristics

36
Q

What were closely related species expected to show?

A

Similar structural features

37
Q

What are the two limitations of using structural differences for classification?

A

Closely related organisms can show different structural features due to adaptive radiation

Distantly related organisms can show similar features due to convergent evolution

38
Q

What is convergent evolution?

A

Convergent evolution is the independent evolution of similar features in species with distinct lineages

39
Q

When may convergent evolution occur?

A

When different species have the same habitat and have the same selection pressures

40
Q

What does shared conditions cause?

A

Common adaptations in different species causing similar structural features

41
Q

What are homologous structures?

A

Traits that are similar because of common ancestry

42
Q

What are analogous structures?

A

Traits that are superficially similar due to common selection pressures but happen through separate evolutionary pathways

43
Q

What has molecular evidence helped scientists show?

A

That species once thought to be closely related due to similar structural features actually showed very different evolutionary origins

44
Q

Why were figworts problematic?

A

Many of the figwort plants had too different structures to function as a meaningful grouping

45
Q

What did the taxonomists examine to split the figwort species into smaller clades?

A

The chloroplast gene

46
Q

What size were figworts before and after reclassification?

A

8th largest to 36th largest

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