18.5 — types of selection

Question 1

what are selection pressures?

Answer 1

enviromental factors that affect an organism’s survival and reproductive success

Question 2

what are some selection pressures?

Answer 2

1. predation
2. competition for resources
3. climate change
4. disease

Question 3

why is the over-production of offspring is important in the process of natural selection?

Answer 3

because it leads to competition for limited resources

Question 4

what happens when there is competition for limited resources?

Answer 4

those best adapted to their environment are more likely to survive, reproduce and pass on their genes — resulting in selection

Question 5

what are the steps in how variation can drive evolution?

Answer 5

1. it generates a range of phenotypes within a population, enhancing the likelihood that some individuals will have advantageous alleles
2. individuals with these traits are more likely to survive and reproduce under changing conditions, transmitting the advantageous alleles alleles to their offspring
3. natural selection occurs

Question 6

what are the three types of natural selection?

Answer 6

directional, stabilising and disruptive

Question 7

what does a graph look like representing directional selection?

Answer 7

look up

Question 8

what does a graph look like representing stabilising selection?

Answer 8

look up

Question 9

what does a graph look like representing disruptive selection?

Answer 9

look up

Question 10

how does directional selection affect phenotypes?

Answer 10

selects one extreme phenotype over other phenotypes

Question 11

how does stabilising selection affect phenotypes?

Answer 11

selects for the average phenotype and selects against extreme phenotypes

Question 12

how does disruptive selection affect phenotypes?

Answer 12

selects for extreme phenotypes and selects against the intermediate phenotypes, especially when an enviromental takes two or more distinct forms

Question 13

what is the effect of directional selection on allele frequency?

Answer 13

increase of allele frequency for one extreme phenotype

Question 14

what type of phenotypes are selected in directional selection?

Answer 14

one extreme phenotype

Question 15

what is the effect on the normal distribution curve in directional selection?

Answer 15

shifts the curve in the direction of the favoured extreme

Question 16

what is an example of directional selection?

Answer 16

antibiotic resistance in bacteria

Question 17

how does stabilising selection effect allele frequency?

Answer 17

it increases allele frequency for the average phenotype, decreases allele frequency for the extremes

Question 18

what phenotypes are selected for stabilising selection?

Answer 18

average phenotypes

Question 19

what is the effect of stabilising selection on the normal distribution curve?

Answer 19

narrows the curve

Question 20

what is an example of stabilising selection?

Answer 20

human birth weights

Question 21

what is the effect of disruptive selection on allele frequency?

Answer 21

increases the allele frequency for multiple extreme phenotypes, decreases allele frequency for intermediates

Question 22

what phenotypes are selected in disruptive selection?

Answer 22

very different extreme phenotypes

Question 23

what is the effect of disruptive selection on the normal distribution curve?

Answer 23

the curve shifts into multiple peaks either side of where the average phenotype peak was

Question 24

what is an example of disruptive selection?

Answer 24

bird peaks adapting to become larger and smaller when there are two different food sources