Selection

Question 1

Model answer for normal

Answer 1

1. Variation caused by mutation leading to different version of allele produced
2. Differential selection pressures such as abiotic / biotic factors
3. Differential reproductive successs as those with advantage phenotype live longer and survive and interbreed to reproduce
4. Overtime increase in allelic frequency for advantageous phenotype

Question 2

3 types of selection

Answer 2

1. Directional = for one extreme
2. Stabilising = for average
3. Disruptive = for both extremes

Question 3

Stabilising selection

Answer 3

For the average
Occurs in stable environment in all populations
Favours the avaege
Eliminate the extremes
Reduces variability
Reduces opportunity for evolutionary change

Question 4

Disruptive selection

Answer 4

1. Selection against abates
2. Both extreme phenotypes have increased reproductive successs so improved survival abd ability to find a mate
3. Allen’s for birth extends passed into future generations in greater numbers
4. Overtime frequency for both Allen’s coding for extreme phenotypes increases.
5. Allele coding for mean phenotype decreases

Question 5

3 sources of genetic variation

Answer 5

1, mutations
2. Meiosis = crossing over and independent segregation
3. Random fertilisation of gamete’s

Question 6

Define allopatric speciation

Answer 6

Formation of new species from different populations in different areas

Question 7

Define sympatric speciation

Answer 7

Formation of new species from reproductive isolation in the same population living in the same area

Question 8

Describe sympatric speciation

Answer 8

1. Not geographically isolated but reproductively isolated as it’s the formation of new species from reproductive isolation living in the same population in the same area but gene pools are separate.
2. By named isolating mechanisms
3. Say which one mates with what
   4, mutation caused by variation forming different Alleles
4. Different Allen’s passed on in each reproductively isolated group
5. Change in allelic frequency
6. This is disruptive selection as favours both extremes
7. Eventually become different species that cannot interbreed to produce fertile offspring’s

Question 9

Describe allopatric speciation

Answer 9

1. Geographically isolated means reproductively isolated as formation of new species from different populations in different areas with separate gene pools
   2, this is allopatric speciation if AO2
2. Mutations causes variation forming differ Allen’s in different populations .
3. Differential selection pressures in each group
4. Diffential reproductive success
5. Changes in allelic frequency
6. Eventuallly become different species which can no longer interbreed to produce fertile offspring

Question 10

Isolating mechanisms (5)

Answer 10

1. Temporal = different feeding / breeding times
2. Behavioural / ecological = differ courtship / niches / habitat
3. Mechanical = mismatch of reproductive parts
4. Hybrid infertility = off number of chromosomes so no meiosis
5. Gamete incompatibility = sperm killed in females or can’t fuse with egg