Selection And Speciation

Question 1

Causes of variation

Answer 1

1. Mutation
2. Meiosis
3. Random fusion of gametes
4. environment

Question 2

Natural selection

Answer 2

Process by which organisms that are better adapted to their environment survive and reproduce in greater numbers

Causing an increase in frequency of the advantageous allele within the population

Question 3

Stabilising selection

Answer 3

Environment is stable
Selection pressure at both ends of distribution
Favours the average
Tends to eliminate extremes
Reduces variability
Reduces opportunity for evolutionary change

Question 4

Directional selection

Answer 4

Mean in population represents optimum phenotype for existing conditions

Environmental change may produce new selection pressure that favours an extreme

over time selection means this allele combination will predominate and the mean phenotype will shift

Question 5

Disruptive selection

Answer 5

Is the opposite of stabilising selection

Environment has selection pressure that favours 2 extreme phenotypes

When conditions change the optimum phenotypes necessary for survival will also change

Question 6

Speciation

Answer 6

The evolution of a new species from existing species

Species are groups of individuals with similar characteristics and same genes which are capable of interbreeding to produce fertile offspring

They belong to the same gene pool

Question 7

What does natural selection lead to

Answer 7

Change in the frequency of Alleles In population

Question 8

What is reproduction isolation

Answer 8

Period when two populations are prevented from interbreeding

To become genetically distinct via an accumulation of mutations and different selection pressure

Question 9

Allopatric speciation

Answer 9

This means any physical barrier which divides a population

Each isolated population may be subject to different selection pressures and adapts over many generations due to natural selection

Mutations accumulate in the different populations

Changes in genotype and phenotype may occur

Eventually when the two populations are reunited, they are now so different that they are unable to interbreed and are reproductively isolated

Each population has become separate species each with its own gene pool

Question 10

Sympathetic speciation

Answer 10

Organisms in the same area to become reproductively separated for other reasons

This could be through choice of food or choice of season to mate in

Question 11

Temporal isolation

Answer 11

Organisms breed at different times of the year

Question 12

Ecological isolation

Answer 12

Different habitats within same area

Question 13

Behavioural isolation

Answer 13

Different behaviour patterns e.g. courtship behaviour

Question 14

Mechanical isolation

Answer 14

Anatomical differences making it impossible for gametes to come together

Question 15

Gametic isolation

Answer 15

Incompatibility between gamete’s prevent hybrid from forming

Question 16

Hybrid isolation

Answer 16

Organisms interbreed but offspring are infertile:

e.g. horse and donkey can produce mule but mule infertile

Question 17

Suggest how two species of palm trees arose by sympatric speciation

Answer 17

1. occurs in the same habitat
2. mutations caused different flowering times
3. reproductive isolation
4. different alleles passed on
5. disruptive selection
6. eventually different species cannot interbreed to produce offspring