Population Differentiation

Question 1

Why does selection not always explain changes in traits in natural populations?

Answer 1

Changes in traits can also result from non-constant environments, movement between populations, and genetic drift acting on neutral loci.

Question 2

How does environmental variability influence genetic traits in populations?

Answer 2

The environment changes over space and time, influencing which traits are favored or neutral depending on location and temporal factors.

Question 3

Why are populations rarely fully isolated?

Answer 3

Individuals, seeds, or gametes often move among populations, causing continuous gene flow.

Question 4

How do loci under strong selection differ from neutral loci?

Answer 4

They show different spatial and temporal patterns due to selective pressures acting on them.

Question 5

What happens to allele frequencies at a neutral polymorphic locus in isolated populations?

Answer 5

Each population experiences independent genetic drift. Outcomes may vary: one population may fix allele A1, another may fix A2, while a third remains polymorphic.

Question 6

Why is population size critical in genetic drift?

Answer 6

Smaller populations experience stronger drift, leading to faster allele fixation or loss and less predictable outcomes across loci.

Question 7

What can long runs of homozygosity in a genome indicate?

Answer 7

They suggest inbreeding within small populations, where individuals breed with close relatives, reducing genetic diversity.

Question 8

What are the long-term effects of drift on small isolated populations?

Answer 8

Loss of genetic diversity, fixation of deleterious alleles, and reduced adaptive potential.

Question 9

What is gene flow?

Answer 9

The movement of genetic material between populations via individuals, seeds, or gametes, changing allele frequencies.

Question 10

How does dispersal distance influence gene flow?

Answer 10

Most individuals disperse short distances, leading to high gene flow locally, while a few travel long distances, affecting genetic variation across larger areas.

Question 11

How does population size influence migration patterns?

Answer 11

Larger populations tend to contribute more migrants, resulting in asymmetrical gene flow when paired with smaller populations.

Question 12

How do migration rates (m) differ from mutation rates?

Answer 12

Migration rates are much larger and affect all alleles at all loci, making migration a powerful force in shaping genetic variation.

Question 13

What does FST measure?

Answer 13

Genetic differentiation between populations, with values ranging from 0 (no differentiation) to 1 (complete differentiation).

Question 14

What do high and low FST values indicate?

Answer 14

Low FST: Populations share similar allele frequencies, indicating high gene flow.

High FST: Populations have distinct allele frequencies, suggesting limited gene flow.

Question 15

How does geographic distance relate to genetic distance?

Answer 15

Generally, greater geographic distance leads to higher genetic differentiation (FST), a pattern known as isolation by distance.

Question 16

When is isolation by distance not expected?

Answer 16

When selection acts on nearby but distinct environments.

When gene flow is extremely high.

When populations have recently been founded or experience frequent local extinctions.

Question 17

How does selection interact with gene flow and drift?

Answer 17

Selection drives differentiation for traits favored in specific environments.

Gene flow counteracts selection by homogenizing allele frequencies.

Drift introduces random variation, especially in small populations.

Question 18

What is QST, and how does it differ from FST?

Answer 18

QST measures differentiation in quantitative traits, with high QST values indicating selection, while FST reflects genetic differentiation in allele frequencies.

Question 19

How can gene flow positively impact populations?

Answer 19

Reduces inbreeding and loss of alleles from drift.

Spreads advantageous alleles across populations.

Enhances adaptive potential by maintaining genetic diversity.

Question 20

What are potential negative effects of gene flow?

Answer 20

Counteracts local adaptation by introducing maladaptive alleles.

Reduces mean fitness if alleles suited for different environments mix.

Question 21

What is a structure plot, and how is it used?

Answer 21

A graphical representation showing the proportion of ancestry from different genetic clusters, used to visualize population differentiation.

Question 22

What factors influence patterns of genetic variation?

Answer 22

Drift, gene flow, selection, population size, and dispersal distances.

Environmental gradients (e.g., temperature, climate).

Question 23

How does migration influence neutral and non-neutral loci?

Answer 23

Migration affects all loci, but selection on non-neutral loci can create patterns distinct from those at neutral loci.

Question 24

What are the key forces shaping genetic variation across landscapes?

Answer 24

Drift: Random changes in allele frequencies.

Gene Flow: Movement and mixing of alleles.

Selection: Favoring traits suited to local environments.