Hardy-Weinberg Population Genetics

Question 1

Define:

• Population
• Gene pool
• Polymorphism

Answer 1

• Population:
  A localised group of interbreeding individuals of the same species
• Gene pool:
  All the alleles of a gene in a population
• Polymorphism:
  Variations/multiple forms of a trait within a population

Question 2

What is the rule for calculating allele frequencies for codominant alleles?

Answer 2

p = dominant allele
q = recessive alleles 

Frequency of p:
2x no. homozygous dominant + no. heterozygotes/total population

Frequency of q:
2x no. homozygous recessive + no. heterozygotes/total population

p + q = 1

Question 3

What is the Hardy- Weinberg Equilibrium?

Answer 3

• Describes the gene pool of population that is not evolving i.e. the allele and genotype frequencies remain constant from generation to generation
  Occurs if:
• every mating is random
• every male gamete unites at random with every female gamete
• frequencies of pairings depend on frequencies of gametes

Question 4

What is the Hardy-Weinberg Principle?

Answer 4

Dominant allele = p
recessive allele = q

Allele frequencies:
p + q = 1

Genotypic frequencies will be:
p^2 +2pq +q^2 = 1

p^2: homozgyous dominant
2pq: heterozygote
q^2: homozygous recessive

Question 5

What are the 5 assumptions underlying the H-W principle?

Answer 5

1. The population is very large:
   - Genetic drift has a significant effect on smaller populations as events by chance that kill certain members of the population will cause a greater fluctuation in allele frequency
2. There is no gene flow:
   - Evolution due to individuals moving into or out of a population
3. There is no natural selection:
   - Individuals with inherited traits better suited to the environment will survive and reproduce more than individuals with a different phenotypic variation of the trait
4. There is no mutation
5. There is random mating:
   - Bias towards similar mate = positive assortment mating
   - Bias towards dissimilar mate = negative assortment mating

Question 6

What is:

• Genetic bottleneck?
• Founders effect?

Answer 6

• Genetic bottleneck:
  When a sudden dramatic decrease in population occurs. Decreases genetic diversity. May fix alleles.
• Founders effect:
  Isolation of a few individuals to form a new population.

Question 7

What is balancing selection?

What are two modes?

Answer 7

• When natural selection maintains two or more forms in the population, occurs by:
  1. Heterozygote advantage: the heterozygote is more fit than both homozygotes under certain conditions
  2. Frequency-dependent selection: The least common genotype is the most fit