Chapter 22.2 - Building a Phylogenetic Tree Flashcards
How is the evolutionary history of organisms determined?
Evolutionary history is determined by building phylogenetic trees based on organism characteristics.
Why are similarities among organisms important in this process?
Similarities among organisms suggest shared ancestry, aiding in the construction of phylogenetic trees.
What caution should be exercised when using shared characteristics for building phylogenetic trees?
Not all shared characteristics are informative; some can be misleading, so careful consideration is necessary.
What are characters in the context of constructing phylogenetic trees?
Characters are the morphological, physiological, or molecular features of organisms used to build phylogenetic trees.
What are character states, and how do they relate to characters?
Character states are the different observed conditions of characters. For example, the presence or absence of a character like lungs or the different arrangements of petals in flowers.
Why can character states in different species be similar?
Character states in different species can be similar either due to common ancestry (homologous) or independent adaptation to similar environments (analogous or convergent evolution).
What is the difference between homologous and analogous character states?
Homologous character states are similar because they originate from a common ancestor, while analogous character states are similar due to independent adaptation to similar selective pressures.
Can you provide an example of homologous character states?
Amniotic eggs in mammals and sauropsids (birds and reptiles) are homologous character states because they originate from a common ancestor.
What is an example of analogous character states?
Wings in birds and bats are analogous character states because they evolved independently in response to similar selective pressures for flight.
How can we determine whether character states are homologous or analogous?
To determine if character states are homologous or analogous, we consider evidence from phylogenetic trees, anatomical or genetic details, and the placement of species on the tree. Homologous character states should have common ancestry, while analogous character states should result from independent evolution.
Why are the details of anatomy and genetic construction important in distinguishing homologous from analogous character states?
The details of anatomy and genetic construction help differentiate between homologous and analogous character states. For example, the anatomy of wings in birds and bats differs, suggesting independent evolution.
What is the difference between homologous and analogous characters, and which is useful for constructing phylogenetic trees?
Homologous characters result from shared ancestry and are useful for constructing phylogenetic trees. Analogous characters arise independently due to similar adaptations and are not used in tree construction.
What is the significance of unique character states in phylogenetic tree construction?
Character states unique to a species or monophyletic group cannot help determine its sister group relationship because they evolved after divergence. They characterize a group but don’t relate it to others.
What are synapomorphies, and why are they important in building phylogenetic trees?
Synapomorphies are shared derived character states that reveal common ancestry among species within a group. They are essential for constructing phylogenetic trees as they help identify sister group relationships.
What is cladistics, and how does it use synapomorphies?
Cladistics is an approach to building phylogenetic trees based on synapomorphies. It seeks to identify shared derived character states to determine evolutionary relationships.
How does the principle of parsimony apply to phylogenetic reconstruction?
Parsimony in phylogenetic reconstruction involves finding the tree with the fewest character state changes to explain the data. It aims to minimize the number of independent mutations needed to account for trait diversity.
What is the role of statistical methods in evaluating phylogenetic hypotheses?
Statistical methods are used to assess the strength of support for a given phylogenetic hypothesis. They help determine the level of confidence in the proposed tree structure based on available character data.
How do biologists handle unresolved branching patterns in phylogenetic trees?
When support for a specific branching pattern is weak, biologists depict unresolved branches, indicating that multiple hypotheses of relationship are possible due to limited data. These patterns represent opportunities for future research.
How are phylogenetic trees constructed using molecular data?
Molecular data, such as DNA or protein sequences, are used to build phylogenetic trees by comparing shared derived characters (synapomorphies) among species or by assessing overall similarity, indicating their evolutionary relationships.
What is the advantage of using molecular data in phylogenetics?
Molecular data provide more characters for phylogenetic analysis compared to morphological data, allowing for finer resolution of evolutionary relationships, especially in organisms with limited morphological information.
What is the assumption underlying distance-based methods in molecular phylogenetics, and why is it less likely to be violated compared to morphological data?
Distance-based methods assume a constant or nearly constant rate of evolution. This assumption is less likely to be violated in molecular data because of the molecular clock hypothesis, which suggests a relatively constant rate of genetic divergence over time.
How do distance-based methods work in molecular phylogenetics?
Distance-based methods in molecular phylogenetics involve counting differences in DNA or protein sequences between species pairs. Fewer differences suggest closer relatedness, while more differences indicate greater evolutionary distance.
How are molecular data and morphological data often used together in phylogenetic analyses?
Molecular and morphological data are frequently combined in phylogenetic analyses, and each can serve as independent assessments of the other. Results from both types of data are usually compatible, especially for organisms rich in morphological characters.
Where can researchers access a substantial repository of molecular data for taxonomic and phylogenetic studies?
GenBank, hosted by the National Institutes of Health, is a major repository of molecular data, providing access to over 100 billion observations (mostly nucleotides) collected under more than 710,000 taxonomic names.
