5.4 Cladistics Flashcards
What is the difference between homologous and analogous structures?
Homologous - appear different, same underlying structure
Ananlogous - features adapted to perform the same function but diff structure
What is a clade?
A group of organisms that have evolved from a common ancestor (include all the species alive today and extinct common ancestors)
Where can evidence for which species are part of a clade be obtained?
From biological molecules to determine how closely related one species is to another
* DNA, RNA, mitochondrion, enzymes
How can DNA be used to identify species?
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
What biological molecules can be used as evidence to compare molecular sequences?
- 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)
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?
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
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?
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
What is the cause of differences in the base sequence of DNA and therefore in the amino acid sequence in proteins?
Mutations
* Accumulate gradually over long periods of time
What are molecular clocks?
Working on the assumption that mutations occur at a relatively constant rate to deduce how long ago different groups split from a common ancestor
Whats the difference between using nuclear DNA and mitochondrial DNA?
Nuclear DNA is ingerited from all ancestors
Mitochondrial DNA (mtDNA) is ingerited from a maternal lineage
What can traits be? (2)
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
What are cladograms?
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
What are cladograms?
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
What is parsimony?
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
What are roots on a cladogram?
The initial ancestor common to al organisms within the cladogram (incoming line shows it originates from a larger clade)
What are nodes on a cladogram?
Each node corresponds to a hypothetical common ancestor that speciated to give rise to two (or more) daughter taxa
What are outgroups in a cladogram?
The most distantly related species in the cladogram which functions as a point of comparison and reference group
What are clades in a cladogram?
A common ancestor and all of its descendants (i.e. a node and all of its connected branches)
What does the numbers on the cladogram represent?
Estimates of population sizes and dates when splits occurred
What does the numbers on the cladogram represent?
Estimates of population sizes and dates when splits occurred
What does it mean if two clades on a cladogram are linked at a node?
They are closely related
What does it mean if two species are only connected via a series of nodes?
They are less closely related
Cladograms can provide strong evidence for what?
For the evolutionary history of a group
Why cant cladograms be regarded as proof?
They are contructed on the assumption that the smallest possible number of mutations occured to account for current base or amino acid sequence diferences
What is cladistics?
The contruction of cladograms and identification of clades
Why was the Figwart family reclassified?
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
Why was the Figwart family reclassified?
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
