Chapter 8!! Flashcards
What are the five assumptions of Hardy-Weinberg equilibrium?
No selection, no mutation, random mating, no migration, and infinite population size (no genetic drift).
What is genetic drift?
A process of random fluctuation in allele frequencies due to sampling error in finite populations.
What are the three main consequences of genetic drift?
- Allele frequencies fluctuate over time, even without selection.
- Some alleles become fixed, others are lost, reducing heterozygosity.
- Separate populations diverge in allele frequencies.
How does population size affect genetic drift?
Smaller populations experience stronger genetic drift, leading to more rapid allele fixation or loss.
What is heterozygosity?
The proportion of individuals in a population that are heterozygous at a given locus.
How does genetic drift affect heterozygosity?
It decreases heterozygosity over time as alleles become fixed or lost.
What is the founder effect?
A type of genetic drift where a new population is established by a small number of individuals, leading to reduced genetic variation.
What is a population bottleneck?
A sharp reduction in population size due to an event, leading to loss of genetic diversity.
What does the neutral theory of molecular evolution predict?
Most genetic variation is due to genetic drift rather than natural selection.
What is effective population size (Ne)?
The number of individuals in a population who actually contribute to the next generation.
If a population of lizards is separated onto small islands due to rising sea levels, how will genetic drift likely affect them over time?
Genetic drift will reduce genetic diversity more quickly in smaller island populations, leading to allele fixation and loss.
A population of birds experiences a bottleneck due to a natural disaster. What genetic consequences would you expect?
Reduced genetic diversity, increased genetic drift, and a higher chance of deleterious alleles becoming fixed in the population.
A species of fish in a small pond has an effective population size (Ne) much smaller than its census population size (N). What could cause this?
Uneven mating success, skewed sex ratios, or fluctuating population sizes reducing the number of individuals contributing to the gene pool.
In a computer simulation, how does population size affect allele fixation due to genetic drift?
Smaller populations show faster fixation or loss of alleles, while larger populations maintain genetic diversity for longer.
A scientist observes that a previously diverse population of plants now has mostly one allele at many loci. What process likely caused this?
Genetic drift, particularly in a small population, leading to allele fixation and loss of heterozygosity.
What does the equation for heterozygosity over time predict about large versus small populations?
Heterozygosity declines faster in small populations, while large populations retain more genetic diversity.
In a study of Argentinian greater rheas, the observed heterozygosity in offspring was lower than expected. What does this suggest?
The effective population size (Ne) is lower than the census population size, meaning fewer individuals are actually reproducing.
How does migration counteract genetic drift?
Migration introduces new alleles, increasing genetic diversity and reducing divergence between populations.
Two isolated island populations of the same species have very different allele frequencies. What evolutionary process explains this?
Genetic drift caused divergence in allele frequencies due to random changes over generations.
In a population of 1,000 individuals, an allele starts at a frequency of 0.5. Will drift likely cause fixation or loss within 10 generations?
Unlikely; in large populations, drift is weak, and allele frequencies remain relatively stable.
In a population of only 10 individuals, an allele starts at a frequency of 0.5. What will likely happen after several generations?
The allele will likely either be completely lost or fixed due to strong genetic drift.
Why do smaller populations tend to have lower heterozygosity over time?
Because genetic drift causes alleles to become fixed or lost more quickly, reducing genetic variation.
Why do some populations lose heterozygosity faster than the model predicts?
Factors like non-random mating, population bottlenecks, and fluctuating population sizes reduce effective population size.
How does the founder effect influence genetic variation in new populations?
It reduces genetic variation since the new population starts from a small, non-representative subset of the original gene pool.
A species of mammals experiences periodic droughts that reduce their numbers significantly. How does this affect their genetic diversity?
Each drought acts as a bottleneck, reducing genetic variation and increasing the impact of genetic drift.
What is the migration-selection balance, and how does it affect local adaptation?
Migration can introduce alleles that are less adapted to the local environment, counteracting selection and preventing full local adaptation.
Why don’t all island populations of banded and unbanded snails become completely unbanded despite selection for crypsis?
Migration from the mainland introduces banded alleles, maintaining variation despite selection.
Why does genetic drift occur even in the absence of natural selection?
Drift results from random sampling of alleles in finite populations, causing unpredictable allele frequency changes.
What is an example of a real-world study supporting the effects of genetic drift on population divergence?
A study on Galapagos lava lizards showed that populations on smaller islands had lower genetic diversity due to drift.
In a population of 50 individuals, an allele frequency starts at 0.5. Over time, what is the likely outcome?
The allele will likely be either completely lost or fixed due to the strong effects of genetic drift in small populations.
What does the neutral theory of molecular evolution say about genetic variation?
It suggests that most genetic variation is neutral and evolves due to genetic drift rather than selection.
How does fluctuating population size affect genetic drift?
When population size varies, genetic drift is strongest during population bottlenecks, accelerating genetic diversity loss.
What is the relationship between effective population size (Ne) and heterozygosity loss?
The smaller the Ne, the faster heterozygosity is lost because fewer individuals contribute to the gene pool.
How do uneven sex ratios affect effective population size?
If one sex contributes disproportionately to reproduction, Ne decreases, increasing genetic drift.
In the conservation genetics problem from the document, what discrepancy was found in the greater rhea population?
Observed heterozygosity was lower than expected, suggesting a lower effective population size than the census size.
If you simulate allele frequency changes in a population of 10,000 individuals, what do you expect to see?
Very little drift; allele frequencies remain stable unless acted on by selection or migration.
What is a population bottleneck, and how does it affect genetic diversity?
A population bottleneck is a drastic reduction in population size due to random events, leading to reduced genetic diversity and increased genetic drift.
What real-world example illustrates the effects of a population bottleneck on genetic diversity?
Northern elephant seals experienced a severe bottleneck due to 19th-century hunting, reducing their genetic variation to almost none, unlike their southern relatives.
How did scientists determine that the loss of heterozygosity in northern elephant seals was due to the bottleneck?
By sequencing museum specimens from before and after the bottleneck, showing a decline from four distinct genotypes to just two.
What is the founder effect, and how does it influence genetic variation?
It occurs when a small group establishes a new population, carrying only a subset of the original genetic variation, leading to increased genetic drift.
What prediction was made about allele diversity in Polynesian crickets on Pacific islands?
Distant island populations were expected to have fewer alleles than nearer islands, reflecting founder effects.
How does the founder effect explain the high frequency of retinitis pigmentosa on Tristan da Cunha?
A rare allele in one of the 15 original settlers became more common due to genetic drift in the small, isolated population.
How does genetic drift contribute to divergence between populations?
Random allele frequency changes over time lead to genetic differences between separated populations, even without selection.
Why did scientists originally struggle to explain the high levels of molecular variation in populations?
Traditional natural selection models couldn’t account for the observed genetic diversity, leading to the development of neutral theory.
What is the neutral theory of molecular evolution, and who proposed it?
Proposed by Motoo Kimura, it suggests that most genetic variation is neutral and evolves due to genetic drift rather than natural selection.
How do neutral mutations differ from beneficial or deleterious mutations in their evolutionary fate?
Neutral mutations are fixed or lost by drift, deleterious mutations are removed by selection, and beneficial mutations may be fixed by selection but can also be lost to drift.
How do mutation types affect molecular evolution rates?
Silent (synonymous) mutations accumulate faster than replacement (non-synonymous) mutations because they do not affect protein function and are not subject to selection.
How does the Ka/Ks ratio help identify positive selection?
If Ka (non-synonymous substitution rate) is higher than Ks (synonymous substitution rate), it suggests positive selection is favoring changes in the protein sequence.
What pattern would indicate purifying selection in a gene comparison between two species?
A Ka/Ks ratio < 1, indicating that most non-synonymous mutations are being removed by selection.
How does the molecular clock hypothesis use neutral mutations to estimate evolutionary time?
Since neutral mutations accumulate at a roughly constant rate, they can be used to estimate divergence times between species.
What is a chronogram, and how is it built?
A phylogenetic tree calibrated with fossil data, allowing molecular divergence to be converted into actual time estimates.
Why are non-coding DNA sequences useful for studying genetic drift?
They evolve primarily through drift rather than selection, providing a more consistent mutation rate.
How do pseudogenes support the neutral theory of molecular evolution?
Since they are non-functional, mutations in pseudogenes evolve neutrally, showing patterns expected from drift rather than selection.
If comparing humans and chimpanzees, what Ka/Ks ratio would suggest adaptive evolution in a specific gene?
A ratio greater than 1, indicating an excess of beneficial non-synonymous substitutions.
Why do some populations experience faster heterozygosity loss than expected?
Factors like fluctuating population sizes, uneven sex ratios, and non-random mating reduce effective population size (Ne).
How does genetic drift interact with natural selection?
Drift can overpower selection in small populations, sometimes leading to the loss of beneficial alleles or the fixation of harmful ones.
