Selection and Genetic Drift

Question 0

What is directional selection?

Answer 0

• if the selection pressure favours those who possess a particular allele, those individuals are placed at a selective advantage
• they will reproduce more frequently and a higher proportion of the next generation will possess that allele
• there is a change in the frequency of alleles
• it is an evolutionary force

Question 1

What is stabilising selection?

Answer 1

• no evolutionary change
• this is because any change away from the well-adapted form is unlikely to be successful and will not pass on more alleles to the next generation
• the alleles that produce these extremes are not likely to increase their proportional share of the gene pool
• there is no change in allele frequency

Question 2

What effect does genetic drift have on small populations?

Answer 2

• the smaller a population the higher the chance that there will be random changes in allele frequency (genetic drift)
• can result in alleles being lost so reduces genetic variation
• may reduce the ability of a population being able to survive in a new environment so could lead to extinction of a species or the production of a new one
• greater effect on population if there has been a population bottleneck (large population suddenly becomes smaller due to a natural disaster)