7 - Phylogeny / Taxonomy Flashcards
1
Q
Systematics
A
- Construction of phylogenies (family trees)
- Determine evolutionary relationships among species, genera, families, etc
2
Q
Taxonomy
A
Using phylogenies to name and classify organisms
3
Q
Phylogeny
A
- Evolutionary relationships among species
- Hierarchical family tree with descendants branching off from ancestors
4
Q
Importance of phylogeny
A
- Basis for identification & classification (taxonomy)
- Helps explain why a species evolved certain adaptations and not others
5
Q
Knuckle walking example
A
- Knuckle walking occurs in chimps and gorillas but not humans
- Because humans and chimps are the closest relatives, Knuckle walking was either present in the ancestor to all three or it developed independently in gorillas & chimps
6
Q
Traditional methods of constructing trees
A
- Looked at overall similarities among species
- Includes both ancestral traits (plesiomorphies), and derived traits (apomorphies)
7
Q
Plesiomorphic
A
Occur in last common ancestor
8
Q
Apomorphic
A
Newly evolved traits (since time of the last common ancestor)
9
Q
Modern methods of constructing trees
A
- Rely on shared derived characteristics to determine relationships
- Cladistics
10
Q
Synapomorphies
A
- Shared derived traits
- Tell us who closest relatives are
11
Q
Symplesiomorphies
A
- Shared primitive traits
- Can’t help us determine who closest relatives are
12
Q
Steps of cladistics
A
- Choose a trait (homologous or analogous)
- Determine polarity of trait (shared primitive or shared derived)
- Repeat step 2 for as many independent, shared derived traits as feasible
- Choose most parsimonious tree
13
Q
Homology
A
- Similar traits shared between organisms because they share a common ancestor
- E.g. frogs & lizards
14
Q
Analogous traits
A
- Similar traits in organisms due to similar function rather than common ancestry
- Through convergent evolution
15
Q
What makes a good trait for claditistics
A
- Homologous
- Objective/quantifiable
- Varies more between than within species
- Independent (not correlated with other traits)
16
Q
How do we know if a trait is primitive (ancestral) or derived
A
- Primitive features tend to be more common
- Look at fossil common ancestors (if the trait is there, it’s primitive)
- Traits that occur earlier in development tend to be primitive (e.g., tail in human embryo)
4. Use an outgroup
17
Q
Outgroup
A
- A species that you know is not closely related to the group of species you are looking at
- If the trait occurs in the outgroup too, it is likely to be primitive
18
Q
Is absence of tials in apes and humans primitive or derived
A
- Having tail is primitive
- Absence of tail is derived for apes/humans
19
Q
Choosing most parsimonious tree
A
- WIth many species, many trees are possible
- Choose the tree with the fewest possible evolutionary steps (especially fewest reversals)
- Based on the principle that simplest solution is most likely (parsimony)
20
Q
Molecular clock
A
- Mutations in genes occur by chance, but over time, accumulating in a regular clock- like manner
- Assumes most changes in genes are small and do not produce effect on phenotype or fitness (neutral theory)
21
Q
Cladistic Taxonomy
A
- Cladists insist descent is only thing that counts for taxonomy
- Chimps and humans are “sister” groups and belong in same clade
22
Q
Evolutionary systematists
A
- Argue descent and overall similarity is important
- Humans should be set apart from apes due to important similarities between African apes and human uniqueness
