1.7 Evolution

Question 1

describe ‘evolution’

Answer 1

evolution is the changes in organisms over generations as a result of genomic variations

Question 2

describe ‘natural selection

Answer 2

Natural selection is the non-random increase in frequency of DNA sequences that increase survival and the non-random reduction in the frequency of deleterious sequences (e.g. sequences the decrease survival).

e.g. some peppered moths have DNA sequences which cause them to be light in colour; light coloured moths are able to camouflage against lichen covered trees so these DNA sequences help moths survive (increases survival), then these sequences are passed on when light coloured moths reproduce

Question 3

describe ‘the 3 types of selection’

Answer 3

Stabilising
- an average phenotype is selected for, extremes of the phenotype of range are selected for
- e.g. clutch size in birds
- too few eggs — the chance of the offspring surviving and passing on genes is low
- too many eggs — parent will be unable to survive for all offspring, some will starve

Directional
- one extreme of the phenotype range is selected for
- e.g. giraffes evolving longer necks
- longer necks are less likely to stare as they can reach the food that is higher on the trees than shorter necks
- genes with longer necks is passed on

Disruptive
- e.g. fur colour in mice
- light and dark fur colours can camouflage against their habitat (e.g. sand and lava flows)
- other fur colours are targeted by predators so are eaten — genes are passed on

Question 4

describe ‘the 2 ways that genes can be transferred’

Answer 4

• vertically (from parents to offspring through sexual or asexual reproduction)
• horizontally (between individuals in the same generation)

Prokaryotes exchange genetic material horizontally.
Eukaryotes exchange genetic material vertically.

Question 5

what is a species?

Answer 5

a group of organisms which are capable of interbreeding to produce fertile offspring and do not normally breed with other groups

Question 6

what is speciation?

Answer 6

the generation of a new biological species by evolution as a result of isolation, mutations and selection

Question 7

describe ‘the main events happening during speciation’

Answer 7

1. Sub-population are isolated by an isolation barrier (ecological, behavioural or geographical).
2. Different mutations arise in each sub-population creating variation.
3. Each population experiences different selection pressures (mutations which increase survival are selected for).
4. After several generations, the sub-populations can no longer interbreed to produce fertile offspring — they are no separate species.

Question 8

why are isolation barriers necessary for speciation to occur?

Answer 8

to prevent gene flow between sub-populations

Question 9

describe ‘the 2 types of speciation’

Answer 9

Allopatric
- involves a geographical barrier (e.g. rivers, mountains and the sea)

Sympatric
- involves an ecological barrier (e.g. pH and salinity)
- involves a behavioural barrier (e.g. for evolution)