Lecture 20: Population structure, gene flow and genetic drift

Question 1

What is gene flow?

Answer 1

Movement of genes from one population to another, typically via migration

Question 2

What is a key difference between natural selection and gene flow taking place in a different environment?

Answer 2

Gene flow always acts to make populations more homogenized to one another no matter if the population lives in a similar environment or not

But if you have natural selection in a different environment, it will act to drive the populations away, and make populations differ. (i.e local natural selection upon a population)

Genetic drift will also cause populations to be different from each other.

Question 3

What is an important property that determines how different populations will be from each other?

Answer 3

Gene flow

Question 4

How does gene flow change between populations? What was an example of the experiment?

Answer 4

Gene flow reduces exponentially as the distance increases, this was seen experimentally by comparing the gene flow between cultivated sunflowers and the weedy ones.

X-axis: Had the frequency
Y axis: The distance in kilometers

Question 5

What is genetic drift?

Answer 5

Random fluctuations happen in allele frequency in random.

GENETIC DRIFT DOES NOT DRIVE evolution in a particular direction.

Question 6

What are the types of Stochastic evolutionary forces?

Answer 6

1. Mutations: Random changes with respect to fitness.
2. Recombination: Shuffling up alleles randomly.
3. Genetic Drift: Random flow of genes

Question 7

What is Deterministic force in Evolution?

Answer 7

Natural Selection: (predictable or non-random evolutionary force)

Question 8

What is a key feature of genetic drift?

Answer 8

It drives to loss of biodiversity. ESPECIALLY when populations are small.

It leads to stochastic changes in allele frequency, due to random changes in fecundity and mortality.

Question 9

What are the examples of Stochastic processes resulting in loss of diversity?

Answer 9

1. Genetic Drift
2. Population Bottleneck
3. Founder effect

Question 10

What is founder effect?

Answer 10

It is colonization by a few individuals that start a new population

The colonizing group contains only a limited diversity compared to the source population.

Question 11

What is population bottle neck?

Answer 11

The sharp reduction in population due to reduction in abundance, is usually followed by a Rebound.

It results in a loss of biodiversity.

Question 12

How does random fluctuation change in allele frequency change with population size?

Answer 12

Genetic drift is more profound when populations are small

More drastic fluctuations in populations

More rapid loss of biodiversity

Faster time for allele loss or fixation

Less consistency across replicate populations.

Question 13

What leads to less genetic diversity in human population in Americas?

Answer 13

More genetic variation is found in Africa, while relatively fewer populations have migrated to Americas, and a series of bottleneck effects lead to low genetic diversity.

Question 14

How does geographic pattern affect population genetic similarity?

Answer 14

Plants closer have more gene flow, and less fixed genes between them

Populations further away have more genetic drift, less gene flow, and are more differentiated than populations that are closer to each other.

Question 15

Why does the human population have relatively no fixed genes between them?

Answer 15

Because they have experienced relatively recent origins and there is more gene flow.

Question 16

Why did the human population differ from east Africa?

Answer 16

East Africa had more gene flow, which was reduced as the migration’s distance increased.

There was more genetic drift in the migrated population.

Question 17

What causes Phenotypic differentiation?

Answer 17

Adaptive OR
Genetic Drift OR
Phenotypic plasticity

Question 18

What is an example of only phenotypic plasticity?

Answer 18

Arrowhead, aquatic plants growing on land differ than those in water, this is only due to genetic plasticity

Question 19

What is phenotypic plasticity?

Answer 19

the ability of a genotype to modify its phenotype in response to the changes to the environment.

Question 20

How does phenotypic plasticity occur?

Answer 20

Occurs through modifications to growth development and behavior. (this is under the control of genetic control)

Question 21

Where is phenotypic plasticity common in?

Answer 21

In sedentary organisms

Question 22

Is phenotypic plasticity adaptive?

Answer 22

not all are adaptive, but usually it is adaptive to unpredictable environment.

Question 23

What were the conclusions from the Clausen-Keck-Heisey Transplant conclusion?

Answer 23

Differences in plants are due to both plasticity and genetics.

There is evidence for widespread local adaptation and local populations had the highest fitness.

Question 24

What are the tradeoffs in human skin pigmentation?

Answer 24

High UV radiation interferes with folate, hence population living there must have been selected for more pigmentation

Low UV radiation, reduced vitamin D synthesis, hence it could have been selected for less pigmentation.

Question 25

Why is there no single ‘best’ phenotype across the globe?

Answer 25

Due to Tradeoff’s.

Question 26

What are other proofs for selection for skin pigmentation?

Answer 26

Alleles affecting the pigmentation have evolved rapidly, (natural selection must have acted)

Genes of pigmentation show one of the highest levels- of population difference than most other genes. Evidence supporting a history of local adaptation.