Lesson test: Chance and drift

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Chance and drift

1.[3p]
Why is drift a force even though its expected effect on $p$ is zero?

The expectation is zero but the variance is not, and there is no term restoring $p$ to where it was

Correct

The expectation is only zero for neutral alleles

The answer is: The expectation is zero but the variance is not, and there is no term restoring $p$ to where it was

Drift always reduces the frequency of rare alleles

The answer is: The expectation is zero but the variance is not, and there is no term restoring $p$ to where it was

Sampling is biased towards common alleles

The answer is: The expectation is zero but the variance is not, and there is no term restoring $p$ to where it was

2.[3p]
With $N = 16$ and $p_{0} = 0.5$ , what variance in $p$ does theory predict after 19 generations?

CorrectNot quite: 0.113

3.[2p]
With $N = 16$ , what fraction of the original heterozygosity remains after 19 generations?

CorrectNot quite: 0.547

4.[3p]
Buri's lines drifted faster than a census of 16 predicts. What quantity belongs in the formula?

The effective population size, which is smaller than the census whenever offspring number varies between parents

Correct

The census size of the offspring generation

The answer is: The effective population size, which is smaller than the census whenever offspring number varies between parents

The number of loci scored

The answer is: The effective population size, which is smaller than the census whenever offspring number varies between parents

The number of generations run

The answer is: The effective population size, which is smaller than the census whenever offspring number varies between parents

5.[3p]
A population sits at 1,000 for four generations and at 10 for one. What is its effective size over the five generations?

CorrectNot quite: 48.1

6.[3p]
A beneficial mutation with $s = 0.05$ appears as a single copy. What is its approximate probability of fixation?

CorrectNot quite: 0.10

7.[2p]
The fixation probability of a beneficial mutation depends strongly on the population size.

True

The answer is: False

False

Correct

8.[3p]
Why does the population size cancel out of the neutral substitution rate?

A population makes $2 N μ$ new mutations and each fixes with probability $1 / 2 N$

Correct

Mutation rates are lower in large populations

The answer is: A population makes $2N\mu$ new mutations and each fixes with probability $1/2N$

Large populations reach fixation faster

The answer is: A population makes $2N\mu$ new mutations and each fixes with probability $1/2N$

Neutral alleles do not fix at all

The answer is: A population makes $2N\mu$ new mutations and each fixes with probability $1/2N$

9.[3p]
Put these proteins in order of increasing rate of amino acid substitution.

Fibrinopeptides
Histone H4
Haemoglobin
Cytochrome c

Show the answer

a, b, c, d

1.[3p] Why is drift a force even though its expected effect on p is zero?

2.[3p] With N=16 and p0=0.5, what variance in p does theory predict after 19 generations?

3.[2p] With N=16, what fraction of the original heterozygosity remains after 19 generations?

4.[3p] Buri's lines drifted faster than a census of 16 predicts. What quantity belongs in the formula?

5.[3p] A population sits at 1,000 for four generations and at 10 for one. What is its effective size over the five generations?

6.[3p] A beneficial mutation with s=0.05 appears as a single copy. What is its approximate probability of fixation?

7.[2p] The fixation probability of a beneficial mutation depends strongly on the population size.

8.[3p] Why does the population size cancel out of the neutral substitution rate?

9.[3p] Put these proteins in order of increasing rate of amino acid substitution.

1.[3p]
Why is drift a force even though its expected effect on $p$ is zero?

2.[3p]
With $N = 16$ and $p_{0} = 0.5$ , what variance in $p$ does theory predict after 19 generations?

3.[2p]
With $N = 16$ , what fraction of the original heterozygosity remains after 19 generations?

4.[3p]
Buri's lines drifted faster than a census of 16 predicts. What quantity belongs in the formula?

5.[3p]
A population sits at 1,000 for four generations and at 10 for one. What is its effective size over the five generations?

6.[3p]
A beneficial mutation with $s = 0.05$ appears as a single copy. What is its approximate probability of fixation?

7.[2p]
The fixation probability of a beneficial mutation depends strongly on the population size.

8.[3p]
Why does the population size cancel out of the neutral substitution rate?

9.[3p]
Put these proteins in order of increasing rate of amino acid substitution.