Lecture 8: Evolution Across Space

Question 1

What is gene flow in simple terms?

Answer 1

Mixing of alleles between different populations

Question 2

What is a cline?

Answer 2

A smooth transition in a trait across geographical space

Question 3

What is clinal variation?

Answer 3

gradual changes in a trait or characteristic of a species across a geographic area

Question 4

Cline vs clinal variation

Answer 4

a cline is the concept of gradual change, while clinal variation is the actual observed variation in traits across different geographical locations

Question 5

How does clinal variation relate to white clover plants?

Answer 5

Some plants have high frequency for an allele that causes deletion of the gene that produces cyanide

Question 6

What is Bergmann’s rule?

Answer 6

Body sizes of mammals and birds tend to increase with distance from the equator

Question 7

Why do animals in cold climates have less heat loss?

Answer 7

larger body size –> lower surface to volume ratio

Question 8

Are moose larger in Northern or Southern Sweden?

Answer 8

Northern

Question 9

What is the Wales mine and common bent grass situation an example of?

Answer 9

Local adaptation

Question 10

Did adult common bent grass or common bent grass grown from seed have higher copper tolerance near the mine?

Answer 10

Adult

Question 11

What happened to tolerance of copper as distance from the mine increased?

Answer 11

Decreased

Question 12

When do clines evolve? (2 answers)

Answer 12

1) When selection pressures change across space

2) When there is gene flow between populations

Question 13

What are the two important roles of gene flow in evolution?

Answer 13

1) Makes populations more similar

2) Introduces new alleles into a population from other populations

Question 14

What causes gene flow?

Answer 14

Dispersal

Question 15

What is dispersal?

Answer 15

Movement of individuals or gametes

Question 16

What affects the ability of toucan subspecies to disperse?

Answer 16

Rivers

Question 17

What is migration rate (m)?

Answer 17

the fraction of individuals arriving from another population each generation

Question 18

Basically, m is a measure of …

Answer 18

how quickly gene flow erodes genetic differences between populations

Question 19

What is the equation for the change in allele frequency before and after migration? What do the variables stand for?

Answer 19

∆p = m(pₘ – p)

∆p: change in allele freq b/c of migration
pₘ: allele frequency in migrants
p: allele frequency in recipient pop
m: migration rate

Question 20

When is migration variance (σₘ^2) used?

Answer 20

When there are no distinct populations and thus the populations are spatially continuous

Question 21

What does σₘ represent?

Answer 21

The average distance between birthplace of a parent and its offspring

Question 22

What does a variance of zero mean?

Answer 22

Measurements are all identical

Question 23

Larger variance means (more/less) dispersal

Answer 23

more

Question 24

Can variance ever be negative?

Answer 24

No

Question 25

What is Fₛₜ and what does it measure?

Answer 25

Fixation index statistic, measures the fraction of total genetic variance across two or more populations resulting from genetic differences between them

Question 26

Fₛₜ = 0 means …

Answer 26

two populations are identical

Question 27

Fₛₜ = 1 means …

Answer 27

two populations are fixed for different alleles

Question 28

Fₛₜ = 0.36 means …

Answer 28

36% of all the genetic variation in the two populations is caused by the differences among them

Question 29

As the distance between pairs of populations increases, Fₛₜ ___

Answer 29

increases

Question 30

selection and gene flow act ___ of each other

Answer 30

opposite

Question 31

What would happen to allele frequencies if there was no selection or drift?

Answer 31

Gene flow would make allele frequencies uniform

Question 32

Gene swamping

Answer 32

When gene flow overwhelms local adaptation

Question 33

What can width of cline be used to measure?

Answer 33

Strength of selection

Question 34

What happens to the cline as the migration variance increases?

Answer 34

Changes in allele frequency are less abrupt, so the cline becomes flatter

Question 35

If selection is stronger than gene flow, then the cline becomes ____

Answer 35

steeper

Question 36

Clines that form when there is selection against heterozygotes are very ___. Why?

Answer 36

narrow. Heterozygotes have reduced fertility