Lecture 7: Population Structure, gene flow, and Genetic Drift

Question 1

Population

Answer 1

group of individuals of single species occupying a given area at the same time

Question 2

Migration

Answer 2

movement of individuals from one population to another.

Question 3

gene glow

Answer 3

movement of genes from one population to another.

Question 4

Key questions for evolutionary studies of variation within populations?

Answer 4

• how much of observed variation among individuals is genetic in origin?
• Does the variation contribute to fitness differences among individuals?

Question 5

How do we measure gene flow?

Answer 5

We have to distinguish between potential gene flow and actual gene flow. We use allozymes (polymorphic genes) as markers because they are neutral/do not affect fitness. If the marker of gene flow was not neutral selection could act against it.

Question 6

What is an experimental way to test gene flow?

Answer 6

Find one homozygous gene in one population and another homozygous gene in another. Watch that loci/gene and if you find heterozygotes you know gene flow has occurred.

Question 7

What was the experimental gene flow observed between crop and weed sunflowers?

Answer 7

Most gene flow occurred over short distance but small amounts occurred as far as 1 km apart.

Question 8

Stochastic Forces

Answer 8

unpredictable, random processes (mutation, recombination, genetic drift)

Question 9

Deterministic Forces

Answer 9

predictable, non-random processes (natural selection)

Question 10

Which stochastic forces result in loss of diversity?

Answer 10

• Genetic drift
• population bottlenecks
• founder events

Question 11

Genetic drift

Answer 11

Random changes in allele frequency due to random variation in fecundity and mortality (important when populations are small).

Question 12

Population bottleneck

Answer 12

sharp, reduction in population size (one time)

Question 13

Founder events

Answer 13

colonization by a few individuals that start a new population with only limited diversity compared to source population.

Question 14

What is likely to happen to allele frequency with genetic drift?

Answer 14

Allele variants are more likely to become fixed in population or disappear completely (allele frequency = 0% or 100%)

Question 15

What happens when there is low gene flow?

Answer 15

differences will accumulate.

Question 16

Characteristic of human genetic variation?

Answer 16

The same, different types of alleles exist across the globe but the frequencies of these alleles differ. Groups of alleles are shared across most populations.

Question 17

Why do human populations out of Africa show evidence of short stretches of neanderthal DNA?

Answer 17

Suggested that humans and neanderthals interbred without sterility or hybrid breakdown either because the differences were slight or the hybrids survived and crossed back and bred with humans (leaving 2% neanderthal DNA)

Question 18

What can cause phenotypic variation?

Answer 18

1. Local adaptation
2. Genetic drift
3. Plasticity

Question 19

Local adaptation

Answer 19

an adaptation a species has to make it better suited to its environment (deer are large in Canada, small in costa rica)

Question 20

Plasticity (in response to environment)

Answer 20

The ability of a genotype to modify its phenotype in response to changes in the environment (deer are small in Costa Rica because they can’t get the right nutrients to grow).
Well developed in sedentary organisms.

Question 21

What are transplant studies?

Answer 21

Involve reciprocal transplants of cloned genotypes into contrasting environments and comparisons of their relative performance (separates between local adaptation and phenotypic plasticity)

Question 22

What was the Clausen-Keck-Hiesey Transect

Answer 22

Transplant experiment done with Potentilla glandulosa done in California. They look plants from coastal, mather and timberline (diff. altitudes) and transplanted each at other altitudes. Timberline and mather plants survived at all altitudes, coastal range plants died at timberline altitude (10 000 ft).

• found that differences between populations are due to plasticity and genetics.
• evidence for local adaptation (local populations had highest fitness)

Question 23

Local adaptation in humans

Answer 23

• skin pigmentation (darker near equator where UV radiation is higher)
• disease resistance
• lactose tolerance
• human height

Question 24

Give an example of phenotypic plasticity

Answer 24

Arrowhead plant (aquatic plant found in Ontario wetlands).