Unit 2 Lecture 8

Question 1

What are the different Modes of Selection (know what they look like on a graph)

Answer 1

1. Directional Selection: When selection favors one or other extreme on the trait
2. Stabilizing Selection: Selection for mean trait value
3. Disruptive Selection: Selection for both extremes

Question 2

Which type of selection is described with the Breeder’s equation?

Answer 2

Directional Selection

Question 3

Explain the variation of Gall Sizes

Answer 3

Gallflies laid eggs in stems of goldenrods, resulting in small and large size galls in the middle of the plant.

Birds tend to eat the larger galls so there was a high mortality for larger gall sizes
Parasitic wasps lay eggs in small galls so there was a higher mortality for small gall sizes

Question 4

What kind of selection is happening in the gall size examples?

Answer 4

Stabilizing because there is selection AGAINST the extremes
- Small gall get parasitized by the wasps
- Large galls get eaten by the bird

Question 5

How do you know if a population has a weak stabilizing selection?

Answer 5

If the mortality is low, then the selection against the extremes is not as strong

Question 6

Explain the study about bristles on flies

Answer 6

They had a population of flies with medium sized bristles with half selecting for larger bristles and the other half selecting for small bristles
What was found was that only flies with high or low number of bristles were allowed to reproduce each generation

Example of disruptive selection

Question 7

Explain the selection in Black Bellied Seedcrackers

Answer 7

• Larger beak depths can handle tough seeds
• Smaller beak depths can handle small seeds

Disruptive selection because there is no selection for the medium size because each beak is needed for the size of the seed

Question 8

When do you use h2 and not H2

Answer 8

Example: measuring both parents and their offsprings
- Parent offspring regression is what gives an estimate of h2

Question 9

How do you calculate S how do you calculate R

Answer 9

S: difference between survivors and original population
R: Difference between offspring and original population

Question 10

The direction of selections depends on ________

Answer 10

Environment

Question 11

When the environment changes, _______ can change

Answer 11

Selection

Question 12

What is the general concept of the two colored mice study

Answer 12

They had clay models of differing colored mice and put them in opposite locations that did not match their coat color. They then saw there were more bite marks on the clay mice who’s fur did not match the ground color.

Different locations (environments) can select for different things

Question 13

What happened when there was a geographic barrier in the mice study

Answer 13

Because of the geographic barrier there was no gene flow

Question 14

Explain the armor plates in sticklebacks study

Answer 14

Sticklebacks either had a high amount of armor plates, low amount of armor plates or large or small lateral spines
- It is harder for predators to eat fish wither armor plates and large lateral spines
- If you’re in an area where there are not a lot of predators, you’ll most likely select against armor plates because they are quite costly

Question 15

Where do armored sticklebacks mainly live? lightly armored?

Answer 15

• Ocean “marine stickleback”
• Lakes “freshwater stickleback”

Question 16

What happens if high armor plated fish invade different lakes?

Answer 16

Overtime they lose their armor
- Spines are not helpful against freshwater predators
- Water chemistry (harder to make armor in freshwater)
- Develop faster without armor

Question 17

What is the allele that selects for armor plated fish?

Answer 17

High-Eda for high plated
Low-Eda for low plates

Question 18

How does the Low-eda allele persist in marine stickleback populations?

Answer 18

The recessive low-end allele will persist because it will be maintained int he population