A3.2 Classification and Cladistics Flashcards
Reasons for classification system
Information storage and retrieval, identification of an organism or species’ name, predictive value/ (characteristics of a species can be predicted from its group), Researching evolutionary origins (grouping species that share traits that evolved from a common ancestor)
Taxa
Groups used to classify organisms (phyla, classes, and orders)
Taxonomy
Assigning organism to taxonomic groups
King Philip came over for good soup.
Kingdom, Phylum, Class, Order, family, genus, species
Disadvantages for Hierarchy of taxa
- can be unclear how populations should be grouped due to the speciation of one species into two.
- There can be disagreement about how species should be grouped into genera or larger groups.
- There can be disagreement about what taxonomic rank a group should have.
- Gradual divergence of species over time makes it hard to objectively determine at what time a species split so taxonomic rankings from domain to genus are inevitably arbitrary.
- The boundary paradox
Ideal Classification
Should follow evolutionary relationships, all members of a taxonomic group have evolved from a common ancestor.
Criteria for ideal classification
- Every organism that has evolved from the same common ancestor is included the same taxonomic group.
- In each taxonomic group, all species have evolved from the same common ancestor.
Importance of Classification criteria
All members if a taxonomic group will have traits inherited from their common ancestor, which allows biologists to create predictions based on classification.
Paradigm
Ideal for demonstrating a theory
Cladistics
An approach to classification in which groups of species that share a common ancestor are identified but are not given a taxonomic rank.
Clade
A group of organisms that have evolved from a common ancestor. (Including ancestral species and all species that evolved from it)
Clade can include many living species, or just a few
True
What do mutations cause?
Differences in the base sequence and therefore the amino acid sequence of proteins.
Over long periods of time between two or more species
Differences in DNA sequences accumulate
Molecular clock methods
A method used to estimate the time since two species diverged from a common ancestor based on the differences accumulated in DNA/amino acid sequences over time, assuming that the differences have accumulated at a constant rate.
The larger the number of sequence differences…
The longer since two species diverged from a common ancestor
Things that effect mutation rate
Generation time, size if the population, intensity of selective pressure.
Most recent common ancestor for humans lived…
Estimated to have lived around 150,000 years ago
Cladogram
A branching diagram that represents ancestor-descendent relationships, and is constructed by sequencing analysis.
Maximum Parsimony
How species could have evolved with the fewest sequence changes.
Terminal branches
Ends that represent individual clades, species or groups that are not subdivided on the cladogram.
Nodes
Branching points in a cladogram that represent the the point at which a hypothetical ancestral species split to form 2 or more clades.
Root
Base of the cladogram and represents the hypothetical common ancestor of the entire clade.
Cladograms that are drawn to scale are based on…
Estimates of the time since each species split
Phylogeny
evolutionary origins
How can we test cladogram accuracy?
Several cladograms can be produced using different genes and checked if they have the same pattern of branching, which ensures the evidence of the evolution is strong.
Hypothesis
A provisional explanation for a pattern
Cladistics on traditional morphology-based classifications of species
- Confirmed that traditional classification corespond to evolutionary relationships in many cases.
- Indicated that the species in a taxonomic group do not all share a common ancestor in some cases.
- Indicates that species with a common ancestor have been placed in different groups in other cases
Three major domains of organisms
Eubacteria, Archaea, and Eukaryotes
