Lecture 6: Phenotypic Evolution (Part 1)

Question 1

Quantitative (phenotypic) traits

Answer 1

Traits that vary continuously and are affected by anywhere from several to thousands of loci

Question 2

Examples of quantitative traits

Answer 2

Crop yield, milk production, body height

Question 3

Genotypic variation is discrete or continuous variation? How?

Answer 3

Discrete, there are only four possible nucleotides (A,C,T,G)

Question 4

Are quantitative traits discrete or continuous variation?

Answer 4

Continuous

Question 5

What type of distribution describes quantitative traits?

Answer 5

Normal distribution

Question 6

What is the shape of a normal distribution?

Answer 6

Bell-shaped curve

Question 7

How are phenotypic traits influenced by the environment?

Answer 7

Environmental factors “smooth off” the curve

Question 8

What are the three modes of selection on quantitative traits?

Answer 8

Directional, stabilizing, disruptive

Question 9

What is directional selection?

Answer 9

favors change in the mean of a trait

Question 10

What is stabilizing selection?

Answer 10

favors individuals near the population mean, which reduces phenotypic variance in the trait

Question 11

What is disruptive selection?

Answer 11

favors the largest and the smallest of individuals

Question 12

Darwin’s finches are an example of which mode of selection on quantitative traits?

Answer 12

Directional

Question 13

Human birth weight is an example of which mode of selection on quantitative traits?

Answer 13

Stabilizing

Question 14

Black-bellied Seedcrackers are an example of which mode of selection on quantitative traits?

Answer 14

Disruptive

Question 15

How does selection in crossbills work?

Answer 15

Kind of selection depends on both phenotypic distribution in birds and the kind of cones they feed on

Question 16

What types of pine cones do Red crossbills eat?

Answer 16

Small hemlock pine cones, large Lodgepole pine cones

Question 17

Correlational selection

Answer 17

Selection that acts on multiple traits simultaneously due to their correlation with one another

Question 18

Beta positive vs beta negative

Answer 18

Beta positive: directional selection favors the mean to increase

Beta negative: selection favors smaller values of the trait

Question 19

What measures the strength of directional selection on a quantitative trait?

Answer 19

selection gradient