U1L7. Drift & Pop. Size

What is the main difference in evolution between small and large populations?

Small populations experience more significant effects from genetic drift than large populations.

What is genetic drift?

Genetic drift is the process of random change in allele frequencies due to sampling effects in finite populations.

What are the three consequences of genetic drift?

1. Fluctuation in allele frequencies. 2. Decrease in heterozygosity within populations. 3. Increase in genetic diversity among populations.

What is a population bottleneck?

A population bottleneck is a sharp reduction in the size of a population due to environmental events or human activities, leading to a loss of genetic diversity.

What is the founder effect?

The founder effect occurs when a small group from a larger population establishes a new population, leading to reduced genetic variation.

How does genetic drift interact with mutation and selection?

Genetic drift can influence the effectiveness of mutation and natural selection by randomly altering allele frequencies, which may enhance or diminish the impact of these processes.

What does the neutral theory of molecular evolution predict?

The neutral theory predicts that most genetic variation is due to random drift of neutral mutations rather than natural selection.

What is demography in the context of evolutionary biology?

Demography is the study of changing structures of populations, including birth rates, death rates, and reproductive sizes.

What is a Wright-Fisher population?

A Wright-Fisher population is a model of a population that is not infinitely large, where interbreeding is random and a parental cohort reproduces and dies leaving the same number of offspring.

What happens to allele frequencies in small populations due to genetic drift?

Allele frequencies can fluctuate significantly due to random sampling effects.

What is the expected outcome of genetic drift over time?

Over time, genetic drift can lead to the fixation or loss of alleles, resulting in reduced genetic variation.

What is the impact of genetic drift on heterozygosity?

Genetic drift typically leads to a decrease in heterozygosity within populations.

How does genetic drift affect diversity among populations?

Genetic drift can increase genetic diversity among different populations, leading to different genotypes.

What is the significance of random change in allele frequencies?

Random change can lead to unexpected evolutionary outcomes, particularly in small populations.

What role do chance events play in genetic drift?

Chance events can significantly influence which alleles are passed on to the next generation, affecting overall genetic diversity.

What is the relationship between population size and genetic drift?

Smaller population sizes are more susceptible to the effects of genetic drift, leading to greater fluctuations in allele frequencies.

What is the effect of genetic drift on isolated populations?

Isolated populations may diverge genetically due to genetic drift, leading to unique evolutionary paths.

What happens to allele frequencies in a population of size 10 due to genetic drift?

In a population of size 10, allele frequencies may fluctuate widely due to the effects of genetic drift.

How does genetic drift contribute to evolutionary change?

Genetic drift can lead to random changes in allele frequencies, which can contribute to evolutionary change over time.

What is the impact of genetic drift on the genetic structure of populations?

Genetic drift can lead to differences in genetic structure among populations, increasing diversity.

What is the significance of the term 'identity by descent' (IBD)?

Identity by descent refers to alleles inherited from a common ancestor, which can affect genetic diversity and population structure.

What is the relationship between genetic drift and neutral alleles?

Genetic drift primarily affects neutral alleles, as it operates independently of natural selection.

How does genetic drift influence evolutionary theory?

Genetic drift challenges traditional views of evolution by highlighting the importance of random processes in shaping genetic variation.

What is the expected outcome of genetic drift in a large population?

In large populations, the effects of genetic drift are minimized, leading to more stable allele frequencies.

How can genetic drift lead to speciation?

Genetic drift can lead to divergence between populations, potentially resulting in speciation over time.

What happens to allele fluctuation as population size increases?

The absolute amount of fluctuation in A1 as a portion of alleles decreases with increases in population size.

How does population size affect the chances of an allele going to fixation?

The chances of an allele going to fixation or loss decrease in smaller populations.

What happens to diversity among populations as population size decreases?

Diversity among populations decreases with decreases in population size.

What does genetic drift cause between populations over time?

Genetic drift causes divergence between populations over time.

What is the initial setup for the populations in the genetic drift simulation?

Each island is seeded with 10 A1A2 individuals, resulting in 10 A1 alleles and 10 A2 alleles at time 0.

What does Sewall Wright's theory state about allele fixation?

The probability that any given neutral allele will drift to fixation is equal to that allele's initial frequency or k/(2N).

How does heterozygosity change as an allele goes to fixation?

Heterozygosity is expected to decrease as an allele goes to fixation.

What is the relationship between population size and inbreeding?

The smaller the population size, the higher the probability of identity by descent (IBD) due to inbreeding.

What is the formula for expected heterozygosity in relation to inbreeding?

Expected heterozygosity is represented as 2pq(1-F); the higher the F, the lower the expected heterozygosity.

What is the expected change in heterozygosity in a Wright-Fisher population?

In a Wright-Fisher population, heterozygosity is expected to decrease by an average of 1/(2N) in each generation.

What happens to heterozygosity during complete selfing?

If a heterozygotic individual is engaged in complete selfing, then N=1, and heterozygosity is halved in every generation on average.

What are observed heterozygosity (Ho) and expected heterozygosity (He)?

Ho is observed by sampling the population, represented as f[A1A2]; He is estimated using the Hardy-Weinberg equation from observed allele frequencies.

What does genetic drift cause to allele frequencies over time?

Genetic drift causes allele frequencies to fluctuate over time.

What is the significance of the number of copies of an allele (k) in a population?

k represents the number of copies of a particular allele in the population and is crucial for calculating fixation probability.

How does genetic drift affect populations of terrestrial animals on different islands?

Genetic drift can lead to divergence between populations of terrestrial animals on different islands over time.

What is the effect of population size on the probability of identity by descent (IBD)?

The probability of identity by descent is 1/(2N), meaning smaller populations have a higher probability.

What is the relationship between inbreeding and expected heterozygosity?

As inbreeding increases, expected heterozygosity decreases.

What does the term 'fixation' refer to in population genetics?

Fixation refers to the process by which a particular allele becomes the only allele present at a locus in a population.

What is the impact of genetic drift on small populations?

Genetic drift has a more pronounced effect on small populations, leading to greater fluctuations in allele frequencies.

What is the expected outcome of genetic drift in large populations?

In large populations, genetic drift has a lesser effect, and allele frequencies are more stable.

What is the formula for expected heterozygosity (He) in a population?

He = 2pq, where p and q are the frequencies of the two alleles.

What does Ho represent in population genetics?

Ho represents the observed heterozygosity in a population.

What is the expected loss of heterozygosity due to genetic drift in a population of 3 million individuals over 48 generations?

1/6,000,000 per generation.

How does the effective population size (Ne) differ from the actual population size?

Ne is typically smaller than the actual population size and accounts for the subset of individuals that contribute to reproduction.

What is the relationship between effective population size and inbreeding?

Effective population size is inversely correlated with the extent of inbreeding.

What is the expected decrease in heterozygosity for a population with Ne of 600?

The loss of heterozygosity was roughly 5,000 times greater than expected by drift.

What factors can skew the effective population size?

Dominant males, skewed sex ratios, and unequal reproductive contributions among individuals.

What is the formula to calculate heterozygosity over time?

At = P(1 + (r/n))^nt, where A is the amount at time t, P is the principal, r is the rate, n is the number of times compounded, and t is time.

What does the term 'inbreeding depression' refer to?

The reduced biological fitness in a population due to inbreeding.

How can temperature affect sex ratios in reptiles?

Temperature during early development determines sex, which can skew ratios and affect Ne.

What is the significance of the Ne/N ratio in population genetics?

It indicates the proportion of the effective population size to the total population size, often averaging around 1/10th.

What is the impact of climate change on sea turtles' breeding?

Warming oceans can lead to skewed sex ratios, producing mostly females without a shift in breeding beaches.

What does Foffspring represent in population genetics?

Foffspring represents the inbreeding coefficient of the offspring generation.

What is the formula for calculating Foffspring considering parental inbreeding?

Foffspring = 1/(2N) + (1 - [1/(2N)])Fparental.

What is the expected heterozygosity in the New Zealand snapper fishery in 1998?

He was approximately 0.769994.

What is the role of demographic factors in effective population size?

Demographics can complicate estimates of Ne due to uneven reproductive contributions.

What is the expected loss of heterozygosity in a stable population over time?

Loss of genetic diversity can occur due to genetic drift, even in large populations.

What is the importance of estimating Ne in fisheries management?

It helps in regulating fish populations to maintain genetic diversity and sustainability.

What does the term 'IBD' stand for in genetics?

IBD stands for 'Identical By Descent,' referring to alleles inherited from a common ancestor.

What can cause a significant drop in heterozygosity in a large population?

Factors like skewed sex ratios and unequal reproductive success can lead to greater loss than expected by drift.

What is the effect of cohort sizes on effective population size?

Cohort sizes can influence Ne by affecting the number of individuals contributing to reproduction.

What is the significance of the study by Frankham (1995) regarding effective population size?

It highlighted that Ne is often much smaller than the censused population size, particularly in vertebrates.

What is the expected heterozygosity drop from ~0.77 to ~0.73 indicative of?

It indicates a significant loss of genetic diversity beyond what would be expected from genetic drift alone.

What is the primary method for estimating effective population size?

Estimating Ne can be done using the expectation that heterozygosity decreases by a factor of 1/(2N) each generation.

What is the effect of small reproductive contributions on heterozygosity?

Even very large populations can rapidly lose heterozygosity when the proportion of the population contributing to reproduction is small.

What is the primary cause of rapid loss of heterozygosity in populations?

Inbreeding.

What mathematical models have scientists developed regarding inbreeding?

Models to calculate the amount of inbreeding, contributions of a parental generation to inbreeding depression (IDB), and the portion of a population engaged in breeding.

What happens to allele frequencies when populations become very small?

Allele frequencies can change dramatically.

What is the term for the phenomenon where allele frequencies change dramatically in small populations?

Genetic drift.

What occurs to variance between generations as a population undergoes a bottleneck?

Variance increases dramatically.

What is the expected outcome when a population returns to a larger size after a bottleneck?

Individual populations stabilize around a new allele frequency but may have diverged dramatically from the original population.

What historical event drastically reduced the population size of northern elephant seals?

A bottleneck in the late 1800s, leaving roughly 10-20 survivors.

How many microsatellite alleles were found in pre-bottleneck northern elephant seals compared to modern ones?

4 microsatellite alleles in pre-bottleneck vs. 2 in modern seals.

What does a comparison of pre-bottleneck specimens and modern seals suggest?

The bottleneck had some effect on genetic diversity, but northern seals might have undergone repeated natural bottlenecks.

What is the harmonic mean in relation to fluctuating population sizes?

It is more or less equal to the harmonic mean of population sizes through time, heavily weighted by the smallest numbers.

How is the harmonic mean calculated?

It is the reciprocal of the mean of the reciprocals of a set of numbers.

What are the effects of population size on genetic drift at various frequencies?

The chances of an allele going to fixation or loss increase in smaller populations.

What is Wright's equation for the probability of fixation under genetic drift?

k/(2N), where k is the number of copies of the allele and N is the total number of alleles.

What is the difference between observed heterozygosity and expected heterozygosity?

Observed heterozygosity is the actual proportion of heterozygotes in a population, while expected heterozygosity is based on allele frequencies.

What is the difference between census population size and effective population size?

Census population size is the total count of individuals, while effective population size accounts for genetic diversity and breeding potential.

What is the immediate effect of a bottleneck on genetic diversity?

It reduces genetic diversity and heterozygosity.

What is the long-term effect of a bottleneck?

It can lead to reduced genetic diversity and increased divergence from the original population.

What does the mtDNA data reflect in terms of genetic diversity?

It measures the number of types in a population; more types indicate more diversity.

What does microsatellite data indicate about genetic diversity?

It counts peculiar repeats in the genome, reflecting genetic diversity.

What role do glycoproteins in the major histocompatibility complex (MHC) play?

They are crucial in initiating the immune response and show a lot of variation.

What is the significance of museum collections in studying genetic diversity?

They provide historical data to compare past and present genetic diversity.