3.7.3: Evolution and Speciation

Question 1

What causes variety in phenotype? (3)

Answer 1

1) Meiosis
2) Random fertilisation
3) Mutation

Question 2

What are the three types of selection?

Answer 2

Disruptive
Directional
Stabilising

Question 3

What is disruptive selection?

Answer 3

• Selection pressures that favour two extreme phenotypes
• Individuals have allele for either extreme trait so are more likely to survive and pass on alleles so more individuals have extreme trait and middle trait allele becomes less frequent.

Question 4

What does continued disruptive selection lead to?

Answer 4

Speciation

Question 5

What is speciation?

Answer 5

Evolution of a new species from an existing species.

Question 6

How does speciation occur?

Answer 6

Two populations undergo a period of reproductive isolation which prevents them from interbreeding. Gene pools will become different through mutations and different selection pressures

Question 7

What is allopatric speciation?

Answer 7

Geographical isolation:
- Physical barrier divides population
- Genetic variation occurs in each population through random mutations and different selection pressures
- Changes genotype and phenotype
- When populations are reunited they are reproductively departed and unable to interbreed as each population becomes its own species in its own gene pool

Question 8

What is sympatric speciation?

Answer 8

• Populations become reproductively isolated due to differences in behaviour
• For example choice of food, choice of mating season, hibernation patterns, courtship rituals
• Random mutations occur so no interbreeding to create fertile offspring
• Two new species formed in the same area