Lecture 13: Natural and artificial selection

Question 1

With discontinuous traits, selection can be analysed by:

Answer 1

• measuring the relative fitness of each genotype.

- Using these fitness values to predict how allele frequencies change.

Question 2

How do we know that natural selection is acting on the quantitive trait?

Answer 2

a) Heritable variation in the trait
b) Competition for resources
c) Differences in fitness that depend on trait

Question 3

E.g. how do we know natural selection occurs with darwin finches re. Beak size??

Answer 3

Heritable? Positive correlation between parents beak size and offspring.
Competition? Seed abundance varies due to drought and wet seasons.
Differences in fitness? Normal distribution graph produced when beak depth vs no. of finches

Question 4

Why doesn’t selection decrease genetic variation (Vg)?

Answer 4

• mutation
• migration
• Hidden genetic variation
• Different forms of selection

Question 5

Directional selection…

Answer 5

Mean shifts but SD stays the same mostly. Shifts the overall population by favouring an extreme.

Question 6

E.g. of directional selection

Answer 6

Flowers:
Larger flowers: more nectar and stronger smell, attracts pollinators.
Nectar robbers prefer smaller flowers not visit day pollinators. Directional selection on a larger spur circle diameter for the flower.

Question 7

Stabilising selection…

Answer 7

Mean stays the same SD changes. (narrows) Acts against extreme phenotypes, favours individuals around mean.

Question 8

E.g. stabilising selection…

Answer 8

New born baby weight, over years come to mean around 7lbs

Question 9

Divergent selection..

Answer 9

Favours variants of opposite extremes. Mean similar, SD changes. 2 or more peaks created. Intermediate restoration must be present

Question 10

Divergent selection needs a restriction in gene flow: (2 e.g.)

Answer 10

• picky about mates? (sympatry)

- Something in the way (allopatry)

Question 11

Sympatry…

Answer 11

two species or populations are considered sympatric when they exist in the same geographic area and thus regularly encounter one another

Question 12

Allopatry…

Answer 12

Occurring in separate, nonoverlapping geographic areas. Allopatric populations of related organisms are unable to interbreed because of geographic separation

Question 13

Directional selection effect on genetic variance?

Answer 13

No effect. no change in Vg

Question 14

Stabilising selection effect on genetic variance?

Answer 14

Decreases Vg

Question 15

Disruptive selection effect on genetic variance?

Answer 15

Increase Vg

Question 16

Natural selection can act on ______ ___ when variation in a heritable trait is correlated with ____

Answer 16

Quantitive traits

fitness

Question 17

The direction of selection can change as the______

Answer 17

environment changes

Question 18

2 examples of artitifical selection

Answer 18

• Brassica oleracea
• -> leads to cabbage, sprouts, broccoli, cauliflower and more
• ->Canis lupus, wolf –> DOGS

Question 19

Artificial selection how do you do it and e.g. (How far can you push it)

Answer 19

Drosophila ‘wildtype’ can fly 2cm/s.

• Use large population (thousands!)
• use the top 10% to reproduce
• (females are faster than males)
• reached 180cm/s by ~80 generation

Question 20

When pushing artificial selection the grap showing generations plateaux, WHY?

Answer 20

Either:

• genetic variation runs out
• or natural selection opposes artificial selection