5.4 Cladistics Flashcards

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1
Q

What is the difference between homologous and analogous structures?

A

Homologous - appear different, same underlying structure
Ananlogous - features adapted to perform the same function but diff structure

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2
Q

What is a clade?

A

A group of organisms that have evolved from a common ancestor (include all the species alive today and extinct common ancestors)

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3
Q

Where can evidence for which species are part of a clade be obtained?

A

From biological molecules to determine how closely related one species is to another
* DNA, RNA, mitochondrion, enzymes

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4
Q

How can DNA be used to identify species?

A

DNA is a biological molecule found in all living organisms
* Its code is universal (it codes for the same amino acid regardless of species)
* Genes can be compared by sequencing the bases in DNA

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5
Q

What biological molecules can be used as evidence to compare molecular sequences?

A
  • Non-coding DNA provides the best means of comparision as mutations will occur more readily in these sequences
  • Gene sequences mutate at a slower rate, as changes to base sequence may potentially affect protein structure and function
  • Amino acid sequences may also be used for comparison, but will have the slowest rate of change due to codon degeneracy (more commonly used to cpmare distantly related species)
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6
Q

What would a species’ base or amino acid sequence look like if they have a recent common ancester vs a common ancestor tens of millions years ago?

A

Recent common ancestor - expected to have a few differences in base or amino acid sequences

Common ancestor long time ago - likely to have many differences

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7
Q

What would a species’ base or amino acid sequence look like if they have a recent common ancester vs a common ancestor tens of millions years ago?

A

Recent common ancestor - expected to have a few differences in base or amino acid sequences

Common ancestor long time ago - likely to have many differences

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8
Q

What is the cause of differences in the base sequence of DNA and therefore in the amino acid sequence in proteins?

A

Mutations
* Accumulate gradually over long periods of time

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9
Q

What are molecular clocks?

A

Working on the assumption that mutations occur at a relatively constant rate to deduce how long ago different groups split from a common ancestor

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10
Q

Whats the difference between using nuclear DNA and mitochondrial DNA?

A

Nuclear DNA is ingerited from all ancestors

Mitochondrial DNA (mtDNA) is ingerited from a maternal lineage

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11
Q

What can traits be? (2)

A

Traits can be analogous or homologous
* Similarities between organisms can either be homologous or analogou
* Homologous structures are similar because of similar ancestry; for example the chilcem wing, human arm and other pentadactyl forelimbs
* Analohous stuctures are similar because of convergent evolution. The human eye and the octopus eue show similarities in structure and function but they are analogous because they evolved independently

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12
Q

What are cladograms?

A

Tree diagrams that show the most probably sequence of divergence in clades
* based on similarities and differences between the species in a clade
* Based on base or amino acid sequences

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13
Q

What are cladograms?

A

Tree diagrams that show the most probably sequence of divergence in clades
* based on similarities and differences between the species in a clade
* Based on base or amino acid sequences

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14
Q

What is parsimony?

A

Calculating how species in a clade could have evolved with the smallest number of changes of base or amino sequence.
* Alothough it does not prove how a clade actually evolved, it can indicate the most probable sequence of divergence in clades
* Carried out by computer

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15
Q

What are roots on a cladogram?

A

The initial ancestor common to al organisms within the cladogram (incoming line shows it originates from a larger clade)

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16
Q

What are nodes on a cladogram?

A

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

17
Q

What are outgroups in a cladogram?

A

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

18
Q

What are clades in a cladogram?

A

A common ancestor and all of its descendants (i.e. a node and all of its connected branches)

19
Q

What does the numbers on the cladogram represent?

A

Estimates of population sizes and dates when splits occurred

20
Q

What does the numbers on the cladogram represent?

A

Estimates of population sizes and dates when splits occurred

21
Q

What does it mean if two clades on a cladogram are linked at a node?

A

They are closely related

22
Q

What does it mean if two species are only connected via a series of nodes?

A

They are less closely related

23
Q

Cladograms can provide strong evidence for what?

A

For the evolutionary history of a group

24
Q

Why cant cladograms be regarded as proof?

A

They are contructed on the assumption that the smallest possible number of mutations occured to account for current base or amino acid sequence diferences

25
Q

What is cladistics?

A

The contruction of cladograms and identification of clades

26
Q

Why was the Figwart family reclassified?

A

After obtaining evidence from biological molecules:
* Found that species in the figwort family were not a true clade
* 5 clades had incorrectly been combined into one family

  • Used to be classified as on eof the largest families in the angiosperms containing over 5000 species
  • Reclassified after analysing chloroplast DNA
  • Now the 36th largest family in the angosperm plants
27
Q

Why was the Figwart family reclassified?

A

After obtaining evidence from biological molecules:
* Found that species in the figwort family were not a trye clade
* 5 clades had incorrectly been combined into one family

  • Used to be classified as on eof the largest families in the angiosperms containing over 5000 species
  • Reclassified after analysing chloroplast DNA
  • Now the 36th largest family in the angosperm plants