# Topic 8.2 - Populations Flashcards

Define allele frequency

How frequently a particular allele appears in a population

Define gene pool

All the alleles of all the genes of all the individuals in a population at any one time

Define genetic bottlenecks

Event that causes big reduction in population

Describe how genetic bottlenecks reduce genetic diversity

- Reduces number of different alleles in gene pool = reduces genetic diversity
- Survivors reproduce and larger population is created from few individuals

Describe how selective breeding reduces genetic diversity

- Individuals with desired characteristics are breed together to pass on the desired alleles
- So alleles (for less desirable characteristics are removed)

- Variety of alleles within population is deliberately restricted to small no. of desired alleles
- Leads to population that possess only desired alleles

What does the Hardy-Weinberg principle predict?

Predicts the frequencies of alleles in a population won’t change from one generation to the next

Name 4 assumptions that the Hardy-Weinberg principle makes

- Population is very large
- Mating is random within population
- There is no selective advantage for any genotype
- There is no mutation

Name the 2 uses of the Hardy-Weinberg equations

- Used to calculate frequency of particular alleles, genotypes and phenotypes within populations
- Used to test whether or not Hardy-Weinberg principle applies to particular alleles in particular population
- If frequencies do change between generations in a large population = influence of some kind

State the Hardy-Weinberg equation for predicting allele frequency

p + q = 1

State the Hardy-Weinberg equation for predicting genotype and phenotype frequency

p squared+ 2pq + q squared = 1

State what p & q represent in this equation:

p + q = 1

- p = frequency of dominant allele A
- q = frequency of recessive allele a

State what p squared, q squared & 2pq represent in this equation:

p squared + 2pq + q squared = 1

- p squared = frequency of homozygous dominant AA
- q squared = frequency of homozygous recessive aa
- 2pq = frequency of heterozygous Aa/aA

The frequency of cystic fibrosis (genotype ff) in the UK is currently approximately 1 birth in every 2500. Estimate the percentage of people in the UK that are cystic fibrosis carriers.

If the frequency of cystic fibrosis is measured 50 years later it might be found to be 1 birth in 3500. Estimate the frequency of the recessive allele (f) in the population.

An allele W, for white wool, is dominant over allele w, for black wool. In a sample of 900 sheep, 891 are white and 9 are black. Calculate the allelic frequencies within this population, assuming that the population is in H-W equilibrium.

q squared = 0.01

q = 0.1

p + 0.1 = 1

p = 0.9