Population Genetics & Natural Selection

Question 1

Why might we need to estimate frequencies of genotypes in a population?

Answer 1

1. To predict how many individuals will inherit a genetic disease
2. To estimate the proportion of individuals who are ‘carriers’ of a genetic disease

Question 2

How do we predict genotypes in a population?

Answer 2

Hardy-Weinberg Equation
p^2 + 2pq + q^2 = 1

p = the frequency of the dominant allele
q = the frequency of the recessive allele

Question 3

Allele frequencies can change via…

Answer 3

• Non-random mating
  - assortive mating
  - inbreeding
• Random genetic drift
• Bottleneck effect
• Founder effect
• Natural selection
• Gene flow or Migration
• Mutation

Question 4

What is random genetic drift?

Answer 4

A random change in allele frequencies due to sampling error over generations

Question 5

What is the bottleneck effect?

Answer 5

This is an example of rapid genetic drift
- The original population has large genetic variation
- Then a population reduction or bottleneck event occurs
- And some alleles are lost or become rare (low genetic diversity)

Question 6

What is the founder effect?

Answer 6

A small population with low genetic diversity that comes from a large population with high genetic diversity

Question 7

Describe the three types of selection

Answer 7

Stabilising selection: reduces variation but does NOT change the mean
Directional selection: changes the mean value towards one extreme
Disruptive selection: favours the two extremes producing two peaks

Question 8

What is frequency dependent selection?

Answer 8

When fitness is dependent on the frequency of the phenotype or genotype in a population (an be negative or positive)
- Negative frequency dependent selection: The more common the phenotype/genotype the worse the fitness
- Positive frequency dependent selection: The more common the phenotype/genotype the better the fitness

Question 9

What is cline?

Answer 9

Spatial distribution of genetic variation.
Cline is the gradual geographic change in genetic/phenotypic composition.

Question 10

Describe how mutation and migration effect the population

Answer 10

Mutation: Very slow to act and usually disadvantageous, its role is usually macroevolutionary proportions
Migration: An individual from another population successfully mates (ie. contributes gametes) to the gene pool.
- brings new alleles
- changes proportions of existing alleles
- changes the population size
- makes two populations more similar to each other