17: Selection + Evolution

Question 1

What is meant by the term species?

Answer 1

• group of organisms with similar physiological, biochemical, behavioural and morphological features
• which can interbreed to produce fertile offspring
• reproductively isolated from other species

Question 2

How might speciation occur?

Answer 2

1. allopatric speciation = geographically isolated
2. no gene flow between populations = seperate gene pools = genetically isolated
3. point of genetic change = mutations, only way to get new alleles
4. different allele frequency, different chromosome numbers = genetic drift
5. different selection pressures in each location, which further changes the allele frequency of the population because different selection pressures will favour different/certain alleles
6. over time, few alleles in each location will be prevalent and the changes in each population to the extent where they cant be recognised as the same species anymore
7. the 2 populations eventually wouldn’t be able to reproduce to make fertile offspring, wouldn’t even mate potentially
8. reproductively isolated, no breeding between them
9. in each location, the organisms which do not possess these favourable alleles will not be fit enough to survive and reproduce, so those unfavourable genes won’t continue in the population

Question 3

What is allopatric speciation?

Question 4

What is sympatric speciation?

Question 5

What is stabilising selection?

Answer 5

eliminates the extremities

Question 6

Factors affecting animal distribution?

Answer 6

1. Food availability
2. Territory
3. temperature
4. water
5. breeding sites

Question 7

Factors affecting plant distribution?

Answer 7

1. soil pH
2. soil salinity
3. nutrient availability
4. temperature
5. water
6. light

Question 8

What is the difference betwene allopatric and sympatric speciation?

Answer 8

allopatric - due to geographical isolation
sympatric - in the same area but different isolating mechanisms