Section 7 - Unit 18: Population genetics

Question 1

Explain how sympatric speciation may occur (3 marks)

Answer 1

• Mutation occurs
• Isolating mechanism, e.g. different breeding seasons / niches / habitats
• Different selection pressures operate / changes in allele frequency

Question 2

Explain how a species can evolve (6 marks)

Answer 2

• Geographical isolation
• No interbreeding
• Variation due to mutation
• Different selection pressures
• Different reproductive success
• Leads to change in allele frequency

Question 3

Give the two types of factors that cause phenotypic variation (2 marks)

Answer 3

• Genetic factors

- Environmental factors

Question 4

What is allopatric speciation (2 marks)

Answer 4

• New species form from different populations

- In different areas

Question 5

What does the Hardy–Weinberg principle predict (3 marks)

Answer 5

• The frequency / proportion of alleles of a particular gene
• Will stay constant from one generation to the next / no genetic change over time
• Providing no mutation / no selection / no migration

Question 6

Explain how resistance to an antibiotic could become widespread in a bacterial population following a gene mutation conferring resistance in just one bacterium (5 marks)

Answer 6

• Frequent use of antibiotic creates selection pressure
• Bacteria with mutation / resistance have (selective) advantage over others
• Reproduce more than other types pass on
• Frequency of advantageous allele increases in subsequent generations
• Frequency of resistant types increases in subsequent generations

Question 7

Suggest how two species could have evolved as a result of sympatric speciation (4 marks)

Answer 7

• Original population living in one area
• Idea of genetic variability
• Concept of reproductive isolation
• Gene pools become increasingly different
• Until interbreeding does not produce fertile offspring

Question 8

Give two assumptions that must be made when using the Hardy-Weinberg equation (2 marks)

Answer 8

• No selective advantage / all genotypes equally fertile
• Large population
• Random mating
• No mutation
• No emigration / immigration

Question 9

Explain how different subspecies of an animal may have evolved from a common ancestor (5 marks)

Answer 9

• No interbreeding / geographic isolation
• Mutation linked to (different) markings/colours
• Selection/survival linked to (different) markings/colours
• Adapted organisms breed / differential reproductive success
• Change in allele frequency

Question 10

Two species of palm tree have arisen via sympatric speciation. The two species diverged from each other
after the island was formed 6.5 million years ago. The flowering times of the two species are different. Using this information, suggest how these two species of palm tree arose by sympatric speciation (5 marks)

Answer 10

• Occurs in the same habitat/environment/population
• Mutation causes different flowering times
• Reproductive separation/isolation
  OR
  No gene flow
  OR
  Gene pools remain separate
• Different alleles passed on
  OR
  Change in frequency of alleles
• Disruptive (natural) selection
• Eventually different species cannot (inter)breed to produce fertile offspring;

Question 11

Describe how sympatric speciation could occur (3 marks)

Answer 11

• Not geographically isolated
• Reproductive isolation OR gene pools remain separate
• Change in allele frequencies
• Therefore can no longer interbreed to produce fertile offspring