Speciation and Genetic Drift

Question 1

What allows speciation to occur?

Answer 1

reproductive isolation, leading to 2 populations (of the same species) that cannot breed together

Question 2

What would reproductive isolation allow to occur?

Answer 2

speciation

Question 3

What are the 2 types of speciation?

Answer 3

allopatric and sympatric

Question 4

What is allopatric speciation?

Answer 4

geographical barriers cause reproductive isolation

Question 5

How would allopatric speciation occur? (5)

Answer 5

• geographical separation
• no gene flow between populations
• different selection pressures
• variation in genes
• different alleles passed on in the different populations
• over time the populations become too different that they can no longer interbreed to produce fertile offspring

Question 6

What is sympatric speciation?

Answer 6

when reproductive isolation is caused by differences in behaviour/non-geographical factors

Question 7

What might cause sympatric speciation?

Answer 7

random mutations that lead to changes in reproductive behaviour such as courtship rituals or seasons of fertility

Question 8

What would different reproductive behaviours cause?

Answer 8

no gene flow between these individuals (sympatric speciation)

Question 9

How does reproductive isolation lead to speciation?

Answer 9

• reproductively isolated populations accumulate different mutations
• DNA is so different that they are too genetically different to interbreed to produce fertile offspring
• classed as 2 different species

Question 10

What is genetic drift?

Answer 10

the change in allele frequency within a population between generations

Question 11

What does substantial genetic drift result in?

Answer 11

evolution

Question 12

What increases the impact changes in allele frequency have on a population?

Answer 12

the size of the population, smaller populations leads to greater impact

Question 13

Why does speciation occur when geographical boundaries prevent populations from breeding?

Answer 13

• environmental conditions/selection pressures are different
• so difference in beneficial alleles

Question 14

How does sympatric speciation occur in plants with different flowering times? (5)

Answer 14

• same habitat/environment
• mutations led to different flowering times
• reproductive isolation so no gene flow
• different alleles passed on/change in allele frequency
• disruptive selection
• overtime, too different so cannot interbreed to produce fertile offspring

Question 15

How would gene flow be impacted by a change in courtship behaviour in 2 populations?

Answer 15

• would not attract/mate with each other
• so no interbreeding
• no gene flow
• could lead to sympatric speciation