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What is the main purpose of using protein sequences in molecular clock analysis?
The molecular clock hypothesis asserts that protein sequences evolve at different rates across species.
False
What is one limitation of the molecular clock hypothesis?
The clock varies across different species and genes due to selection pressure.
According to amino acid substitution rates, __________ has the fastest rate of substitution.
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Which protein has the slowest amino acid substitution rate?
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Match the following proteins with their corresponding amino acid substitution rates:
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Who introduced the Relative rate test for molecular clock analysis?
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According to the neutral theory of molecular evolution, what is the main cause of evolutionary change?
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What is the primary focus of molecular phylogeny?
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The molecular clock hypothesis suggests that protein sequences evolve at variable rates across different species.
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What is phylogeny?
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The molecular clock hypothesis was proposed by Zuckerkandl, Pauling, and Margoliash in _____ and _____ (years).
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Match the following terms with their definitions:
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Which one of the following assumptions is NOT a part of phylogenetic analysis?
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The study of changes in genes and proteins is an integral part of molecular evolution.
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What did Early research by Dayhoff focus on with regard to molecular phylogeny?
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What is the purpose of the Tajima Relative Rate Test?
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The molecular clock hypothesis suggests that all sequences should have varying rates of evolution.
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What statistical method does the Tajima Relative Rate Test employ to determine the comparability of evolutionary rates?
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The Tajima algorithm uses a common ancestor, denoted as ______, to analyze the rates of change.
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Match each evolutionary theory usage with its correct description:
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What is indicated when the MC hypothesis is rejected?
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Branch lengths in a phylogenetic tree represent the time elapsed between nodes.
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What does a phylogenetic tree diagram represent?
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Study Notes
Molecular Clock Hypothesis
- Proposed in 1962 & 1963 by Zuckerkandl, Pauling and Margoliash
- States that the rate of molecular evolution is constant for a given protein or gene in all lineages
- The constant rate of molecular evolution allows for the estimation of divergence times between sequences
- Amino acid substitution rates are constant across proteins
- Studied using human globins with known amino acid composition.
Dickerson (1971)
- Similar experiments were conducted using globins in 1971 by Dickerson
- Used proteins with known palaeontological data
- Demonstrated that proteins evolve at consistent rates
Tajima's Relative Rate Test (1993)
- Introduced a test for the molecular clock hypothesis
- Calculates the relative rates of evolution of two proteins or protein families
- Adds a third protein as an outgroup
- Uses a common ancestor to determine rates of change
- Employs the null hypothesis to accept or reject the clock hypothesis
Tajima Algorithm
- Uses three sequences, with one being the outgroup
- Accounts for alignment, with each nucleotide position represented by a number
- Uses the molecular clock to indicate equal evolution rates across all sequences, regardless of the substitution model
- Evaluates whether the rates of change are consistent across all sequences
- If rates deviate significantly, the molecular clock hypothesis is rejected
Uses of Evolutionary Theory
- Important for gene family identification and gene discovery
- Can be used to investigate the origins of genetic diseases and the epidemiology of pathogenic diseases
- Aids in the characterization of genetic polymorphisms
- Contributes to evolutionary theories of life
Phylogenetic Tree Diagrams
- Consists of branches and nodes
- Nodes represent common ancestors, homologies, or evolutionary relationships
- Branch lengths reflect the degree of these relationships
- Branch lengths can indicate the number of changes occurring between nodes
- Can be represented as a distance scale on the tree
Tree Topology
- Refers to the relationship of the tree subjects
- Describes the arrangement of the nodes
- Can indicate common ancestors, homologies, or evolutionary relationships
Limitations of the Molecular Clock Hypothesis
- The rate of evolution varies across different species, genes and parts of individual species
- Selection pressure and generation time can affect the clock
- Morphological and molecular evolution may not necessarily have correlated rates
- The clock only works if the gene or protein function remains consistent over evolutionary time.
Kimura's Neutral Selection Theory (1968)
- The main cause of evolutionary change is random drift of mutant alleles
- These mutant alleles are selectively neutral, thus the variation is not directly affected by natural selection
- The clock is affected by many factors including: metabolic rates, generation times, population sizes, mutation rates, and selection pressures
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Description
Explore the molecular clock hypothesis, which asserts that molecular evolution occurs at a constant rate across different lineages. This quiz covers significant experiments from Zuckerkandl, Pauling, Margoliash, and Dickerson, as well as Tajima's relative rate test. Test your understanding of the principles and applications of this important concept in evolutionary biology.
