7.3

Question 1

Give three examples of selectional pressures

Answer 1

Competition
Disease
Predation

Question 2

What do selection pressures determine?

Answer 2

Allele frequency in a gene pool

Question 3

What causes variation in a population?

Answer 3

Genetic factors

Environmental factors

Question 4

What are the sources of genetic variation?

Answer 4

Mutations
Meiosis
Random fertilisation

Question 5

How does variation as a result of genetics alone compare to variation as a result of genetics and environment statistically?

Answer 5

Genetics alone- discontinuous variation- bar chart

Genetics + environment- continuous variation- normal distribution curve

Question 6

How do selectional pressures result in natural selection?

Answer 6

Variation occurs within a species due to genetics variation
Selectional pressures create struggle for existence
Individuals who have a selectional advantage due to having advantageous phenotypes will be better adapted to the environment so more likely to survive so more likely to pass on favourable alleles
If selectional pressures don’t change, offspring with favourable alleles more likley to survive and pass on
Frequency of beneficial allele will increase in gene pool over successive generations

Question 7

What are the three types of natural selection?

Answer 7

Stabilising
Directional
Disruptive

Question 8

What kind of environment does stabilising selection occur in? What does this mean for variation? How is this shown on a distribution curve?

Answer 8

Very stable
Extremes not selected for so variation decreases
Narrow curve, mean remains the same

Question 9

What kind of environment does directional selection occur in? What does this mean for variation? How is this shown on a distribution curve?

Answer 9

Changing environment
One extreme selected for in favour of the other extreme so variation increases
Curve moves one way or another, mean changes as optimum survival value changes

Question 10

What kind of environment does disruptive selection occur in? What does this mean for variation? How is this shown on a distribution curve?

Answer 10

Environment with two distinct forms
Both extremes selected at the expense of intermediate phenotypes so variation increases
Two curves that dip at the mean

Question 11

Which is the least common type of natural selection?

Answer 11

Disruptive

Question 12

Which type of natural selection results in the most evolutionary change?

Answer 12

Disruptive

Question 13

How does a populations environment affect allele frequency? (3)

Answer 13

Selection pressures within environment
Favourable alleles that code for advantageous phenotypes more likely to survive
Frequency of favourable alleles increases within gene pool as they are passed on

Question 14

Define speciation

Answer 14

Formation of a new and distinct species through the process of evolution

Question 15

How do new species form?

Answer 15

Portion of existing species needs to change so no longer has significantly similar characteristics so can’t interbreed

Question 16

What two things does speciation require?

Answer 16

Isolation = population separated due to change in climatic condition that produces a body of water that separates the habitat
Different selectional pressures

Question 17

What is it called when speciation occurs due to geographical isolation?

Answer 17

Allopatric speciation

Question 18

How does speciation occur due to geographical isolation?

Answer 18

Adaptive radiation= diversification of a group of organism into forms that fill an ecological niche within a given habitat
Leads to change in allele frequency in each population
Each population evolves

Question 19

What is it called when speciation occurs due to behavioural or mechanical isolation in a population in the same area?

Answer 19

Sympatric isolation

Question 20

How does speciation occur through a genetic niche?

Answer 20

Happens in small populations- small gene pool
Genetic diversity restricted as only a small number of allele types to be passed around
Any new alleles that arise through mutation and are a selectional advantage will quickly increase in frequency in subsequent generations
Effects of genetic drift will happen quickly within small population

Question 21

Why doesn’t speciation due to a genetic niche occur in large populations?

Answer 21

Larger gene pool so any changes less pronounced so more allelic variety
Generic drift effects and new species development will be much slower