Problem Set 2 Flashcards
Why are natural selection (NS) and genetic drift considered critically important evolutionary forces?
- Natural selection and genetic drift are critical evolutionary forces because they drive changes in allele frequencies within populations over time, leading to evolution.
- Natural selection promotes the survival and reproduction of individuals with advantageous traits, thereby increasing the frequency of those traits in the population.
- Genetic drift, is a random process that can lead to significant changes in allele frequencies, especially in small populations, potentially resulting in the loss of genetic diversity.
What forces can lead to NS?
Environmental Factors: Changes in climate, availability of resources, and presence of predators can affect which traits are advantageous.
Sexual Selection: Preferences for certain traits in mates can drive the evolution of those traits.
Competition: Competition for resources can lead to the selection of traits that enhance survival and reproduction.
Mutations: New mutations can introduce variation that may be subject to natural selection.
What types of NS do you know?
Directional Selection: Favors one extreme phenotype over others, leading to a shift in the population’s trait distribution.
Stabilizing Selection: Favors intermediate phenotypes and reduces variation, maintaining the status quo for a particular trait.
Disruptive Selection: Favors extreme phenotypes at both ends of the spectrum, potentially leading to speciation.
Sexual Selection: A form of natural selection where individuals with certain traits are more likely to attract mates.
How can alleles that are lethal in certain environments be maintained in a population? (Remember that the rest of the genome can be considered as the environment to a given allele)
Heterozygote Advantage: If individuals who are heterozygous for a lethal allele have a fitness advantage in certain environments, the allele can persist in the population.
Environmental Variation: In fluctuating environments, the lethal allele may confer advantages in some conditions while being detrimental in others, allowing it to be maintained.
Mutation: New mutations can reintroduce lethal alleles into the population.
Genetic Drift: In small populations, random fluctuations can allow lethal alleles to persist despite their negative effects.
Can gene flow prevent or speed up evolution?
Preventing Evolution: Gene flow can introduce new alleles into a population, reducing differences between populations and counteracting the effects of natural selection and genetic drift.
Speeding Up Evolution: If gene flow introduces advantageous alleles from one population to another, it can accelerate adaptation and evolutionary change.
What is genetic drift? How does it work? Explain bottleneck and founder effect.
Genetic drift is a random process that causes changes in allele frequencies in a population due to chance events. It is particularly significant in small populations where random events can have a larger impact.
Bottleneck Effect: Occurs when a population undergoes a drastic reduction in size due to an event (e.g., natural disaster), leading to a loss of genetic diversity. The surviving population may not represent the genetic diversity of the original population.
Founder Effect: Occurs when a small group of individuals establishes a new population. The new population may have different allele frequencies compared to the original population, leading to reduced genetic diversity and potential fixation of certain alleles.
What is the Hardy-Weinberg equilibrium? What is it used for? What conditions can break the HW equilibrium?
The Hardy-Weinberg equilibrium is a principle that describes the genetic variation in a population that is not evolving. It provides a mathematical model to predict allele and genotype frequencies under certain conditions.
Uses: It is used as a null hypothesis to determine whether evolution is occurring in a population.
Conditions that can break HW equilibrium:
- Non-random mating
- Natural selection
- Genetic drift
- Mutation
- Gene flow
Explain some of the real-life examples of deviations from HW discussed in class.
Inbreeding: In small populations, inbreeding can lead to increased homozygosity and reduced genetic diversity.
Natural Selection: Populations experiencing selective pressures (e.g., antibiotic resistance in bacteria) show changes in allele frequencies that deviate from HW predictions.
Genetic Drift: Small populations, such as island populations, may experience significant genetic drift, leading to deviations from HW equilibrium.
How can mitochondrial DNA and the Y chromosome help us track lineages? How can they help us understand human evolution?
Mitochondrial DNA: Inherited maternally, mtDNA can be used to trace maternal lineages and study population genetics over generations. It is particularly useful for understanding human migration patterns and evolutionary history.
Y Chromosome: Inherited paternally, the Y chromosome can be used to trace paternal lineages. It provides insights into male-specific ancestry and can help identify population structure and migration events.
Both mtDNA and the Y chromosome have relatively low mutation rates, making them valuable tools for studying human evolution and the relationships between different populations over time. They can reveal patterns of migration, adaptation, and genetic diversity among human populations.
