Week 5: Sources of evolution and change

Question 1

What are the causes of evolution that ARE NOT selection?

Answer 1

• Mutation
• Gene flow
• Genetic drift

Question 2

What is a mutation?

Answer 2

• A heritable change in the nucleotide sequence that can occur spontaneously
• Can be harmful, neutral or beneficial

Question 3

What are the different types of mutations?

Answer 3

• Substitutions: change one base for another
• Deletion: remove a base/ shift the sequence
• Insertion: adding a base/ shift the sequence
• Inversion: a chunk is flipped around and put back into the strand

Question 4

What is gene flow?

Answer 4

Introduction or loss of new alleles into the population through immigration or emigration

Question 5

What is genetic drift?

Answer 5

Change in gene frequency in a population due to random events

Question 6

Describe the effects of genetic drift.

Answer 6

• Can cause a population bottleneck
• The probability that an allele drifts to fixation is the same as its frequency in the population
• The rate of drift depends on population size

Question 7

What is the founder effect?

Answer 7

• when a new population is founded from a bottleneck
• Small founder populations may have a non-representative sample of genes

Question 8

Which equation is used to measure parental genotype frequency and why?

Answer 8

p + q = 1
p is A1, q is A2
We assume random mating and no selection

Question 9

What do we have to assume in order to use the Hardy Weinberg equation?

Answer 9

• There’s a large population
• There’s random mating
• There’s no selection

Question 10

What is the Hardy Weinberg Equilibrium?

Answer 10

p² + 2pq + q² = 1

Question 11

Describe the strength of selection.

Answer 11

• Variation in selection coefficient (chance of survival to reproduction) affects rate of evolution

Question 12

Describe directional selection.

Answer 12

• Selection is towards a particular direction
• Individuals on one side of the distribution are favoured
• Population evolves in this direction

Question 13

Describe stabilizing selection.

Answer 13

• Most common in nature
• Average members of the population are favoured over extremes
• Example is birth weight in humans

Question 14

Describe disruptive selection.

Answer 14

• Individuals in the middle compete with both sides of the distribution
• Intermediates are disfavoured

Question 15

How do you calculate total variation in the population?

Answer 15

Total variation = genetic var. + environmental var.

Question 16

How do you calculate heritability?

Answer 16

H = additive gene variance/ phenotypic variation
OR H = gene var. in trait/ total var.