Lecture 7

Question 1

Directional Selection

Answer 1

• when one extreme phenotype is favored by natural selection

- changes the average value of a trait

Question 2

example of directional selection

Answer 2

swallows: directional selection caused average body size to increase

Question 3

Stabilizing Selection

Answer 3

-reduces the amount of variation in a trait

Question 4

example of stabilizing selection

Answer 4

birth weight of humans, very small and very large babies are more likely to die leaving a narrower distribution of birth weights

Question 5

Disruptive Selection

Answer 5

maintains or increases the amount of variation in a trait

-extreme phenotypes are favoured

Question 6

Example of Disruptive Selection

Answer 6

Lazuli Bunting birds: colourful males compete with the intermediate color males, leaving the dull colored males with less competition

Question 7

Negative Frequency Dependent Selection

Answer 7

fitness is high in rare phenotypes

Question 8

Example of negative frequency dependent selection

Answer 8

snakes: birds know what typical snakes look like so they feed on those rather than uncommon looking snakes

Question 9

Positive frequency dependent selection

Answer 9

common phenotypes are more favoured

Question 10

Genetic Drift

Answer 10

any change in allele frequency in a population over time due to chance

Question 11

Fixation

Answer 11

gone from a variable to everyone in the population containing that allele

Question 12

Characteristics of Genetic Drift

Answer 12

• more pronounced in small populations
• unbiased with respect to fitness
• not adaptive
• causes allele frequencies to drift up and down randomly over time

Question 13

Population Bottlenecks:

Answer 13

can eliminate allele types, even though the population can be recovered, there is less variation

Question 14

Founder Effects

Answer 14

subset of a population that migrates to a different area and brings a subset of the genetic variation