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Evolutionary Biology Concepts
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Evolutionary Biology Concepts
Evolutionary Biology Concepts
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1
Question
How have evolutionary concepts like common ancestry and natural selection been applied to the study of HIV?
Answer
Common ancestry helps trace the virus's origins, showing that HIV evolved from simian immunodeficiency virus (SIV) transmitted to humans from primates. Phylogenetic studies map the viral lineages and track their global spread. Natural selection explains how HIV evolves within hosts, particularly in response to antiretroviral drugs, with mutations that allow the virus to survive drug treatment becoming more common, leading to drug-resistant strains. HIV also evolves to evade the immune system.
2
Question
What is the classical definition of homology?
Answer
The classical definition of homology refers to the similarity between traits in different species due to shared ancestry.
3
Question
How has the definition of homology changed since Darwin?
Answer
Since Darwin, the definition of homology has evolved to emphasize that homologous traits arise through descent with modification. These traits may serve different functions but are inherited from a common ancestor. Modern genetics recognizes that even structures with little outward resemblance can be homologous if they share a similar developmental origin or genetic basis.
4
Question
What are some examples of molecular homologies?
Answer
1. DNA Sequences: Genes that are conserved across species due to common ancestry, like the Hox genes, which control body plan development in animals. 2. Proteins: Homologous proteins, such as hemoglobin, found in various organisms. 3. Ribosomal RNA (rRNA): Highly conserved across all domains of life, indicating a shared evolutionary origin.
5
Question
What is an atavism?
Answer
An atavism is the reappearance of a trait in an organism that was present in its evolutionary ancestors but has been lost in more recent generations. Examples include humans born with a small tail (coccygeal projection) or whales with rudimentary hind limbs.
6
Question
What is a phylogeny?
Answer
A phylogeny is a diagram or tree that represents the evolutionary relationships among different species or groups, showing how species are related through common ancestry and the sequence of their divergence over time.
7
Question
Define apomorphy and provide an example.
Answer
Definition: A derived trait that has evolved in a particular lineage and distinguishes it from its ancestors. Example: The development of feathers in birds is an apomorphy relative to their reptilian ancestors.
8
Question
Define plesiomorphy and provide an example.
Answer
Definition: An ancestral trait shared by a group of organisms but also present in distant ancestors. Example: The presence of vertebrae in both fish and mammals is a plesiomorphy, inherited from a common vertebrate ancestor.
9
Question
Define synapomorphy and provide an example.
Answer
Definition: A shared derived trait that is unique to a particular group of organisms and their most recent common ancestor. Example: Mammary glands are a synapomorphy that unites all mammals.
10
Question
Define monophyletic clade and provide an example.
Answer
Definition: A group of organisms that includes a common ancestor and all of its descendants. Example: The group Mammalia is monophyletic because it includes the common ancestor of all mammals and all its descendants.
11
Question
Define polyphyletic clade and provide an example.
Answer
Definition: A group of organisms that does not include their most recent common ancestor. Example: Flying animals like bats and birds form a polyphyletic group because their most recent common ancestor did not have wings.
12
Question
Define paraphyletic clade and provide an example.
Answer
Definition: A group that includes a common ancestor but not all of its descendants. Example: Reptiles excluding birds form a paraphyletic group because they share a common ancestor with birds, but birds are not included.
13
Question
Define parsimony and provide an example.
Answer
Definition: The principle that the simplest explanation or phylogeny, with the fewest evolutionary changes, is preferred. Example: The phylogeny that requires the fewest evolutionary changes to explain shared traits is considered the most parsimonious.
14
Question
Define convergence and provide an example.
Answer
Definition: The evolution of similar traits in unrelated lineages due to similar environmental pressures, not common ancestry. Example: Wings in bats and birds are examples of convergent evolution.
15
Question
Define reversal and provide an example.
Answer
Definition: The reappearance of an ancestral trait in a descendant that had previously lost it. Example: Some snakes have vestigial limbs, representing a reversal to an ancestral tetrapod condition.
16
Question
Define homoplasy and provide an example.
Answer
Definition: A trait that appears similar between species but is not due to shared ancestry; can result from convergence or reversal. Example: The streamlined body shape of dolphins and sharks is a homoplasy, resulting from convergent evolution.
17
Question
How have phylogenies been used to test hypotheses?
Answer
1. Confirming Common Ancestry: Showing relationships, like birds evolving from theropod dinosaurs. 2. Biogeography: Testing species distributions and explaining current geographic patterns. 3. Trait Evolution: Mapping the evolution of traits, such as wings in bats and birds. 4. Co-evolution: Comparing host and parasite trees to test if they evolved together. 5. Molecular Clocks: Estimating divergence times using mutation rates. 6. Conservation: Prioritizing species that are evolutionarily distinct for protection.
18
Question
What is the difference between maximum likelihood and parsimony in phylogenetic analysis?
Answer
Maximum likelihood evaluates the probability of a tree given a specific model of evolution, selecting the tree that maximizes the likelihood of observing the data. Parsimony selects the tree that requires the fewest evolutionary changes, assuming simpler explanations are more likely to reflect true evolutionary history.
19
Question
What is the molecular clock and how is it used?
Answer
The molecular clock is a method used to estimate the time of evolutionary events based on the rate of genetic mutations. It is used by comparing genetic differences between species to estimate divergence times, calibrating with fossil records, and constructing phylogenetic trees.
20
Question
What are Darwin's four postulates for evolution by natural selection?
Answer
1. Variation: Individuals within a population must exhibit variation in their traits. 2. Inheritance: The traits that vary among individuals must be heritable. 3. Differential Survival and Reproduction: Individuals with advantageous traits are more likely to survive and reproduce. 4. Struggle for Existence: There must be competition for limited resources.
21
Question
What are the three major modes of natural selection?
Answer
1. Directional Selection: Favors one extreme phenotype, shifting the population toward that trait. 2. Stabilizing Selection: Favors intermediate phenotypes and selects against extremes, reducing variation. 3. Disruptive Selection: Favors both extreme phenotypes while selecting against intermediates.
22
Question
What are the assumptions of the Hardy-Weinberg theorem?
Answer
1. Large Population Size: The population must be large enough to minimize genetic drift effects. 2. Random Mating: Individuals must mate randomly with respect to the trait. 3. No Mutation: No new mutations affecting the alleles. 4. No Migration: No individuals enter or leave the population. 5. No Natural Selection: All individuals have equal fitness.
23
Question
What is genetic drift and how does its importance depend on population size?
Answer
Genetic drift is a random process that leads to changes in allele frequencies within a population over time due to chance events. Its importance is heightened in small populations where random events can significantly alter allele frequencies; in larger populations, the effects are diluted.
24
Question
What were the key findings of Buri's experimental study on genetic drift in Drosophila melanogaster?
Answer
1. Allele Fixation: In many populations, one allele became fixed while the other was lost, demonstrating genetic drift's role in the loss of genetic variation. 2. Random Fluctuations: Allele frequencies changed randomly due to chance events. 3. Population Variability: Different populations showed varying outcomes in allele fixation, emphasizing drift's ability to produce divergent evolutionary paths.
25
Question
What leads to reduced genetic diversity and random fixation of alleles in populations?
Answer
Populations can lead to reduced genetic diversity and random fixation of alleles.
26
Question
How is the fixation probability of an allele under drift related to the initial frequency of the allele?
Answer
The fixation probability of an allele under genetic drift is directly related to its initial frequency in the population.
27
Question
What is the fixation probability of an allele with a higher initial frequency?
Answer
An allele that starts at a higher frequency has a greater chance of becoming fixed, reaching 100% frequency in the population.
28
Question
What is the fixation probability of an allele with an initial frequency of 80?
Answer
If an allele has an initial frequency of 80, its probability of fixation is approximately 80%.
29
Question
What is the fixation probability of an allele with a lower initial frequency?
Answer
An allele with a lower initial frequency has a lower probability of fixation.
30
Question
What is the fixation probability for an allele at 20 frequency?
Answer
An allele at 20% frequency has about a 20% chance of becoming fixed.