3.3.7 Allele Frequencies in Populations Flashcards Preview

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Flashcards in 3.3.7 Allele Frequencies in Populations Deck (16)
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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

  1. Used to calculate frequency of particular alleles, genotypes and phenotypes within populations
  2. 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

p2 + 2pq + q2 = 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 p2, q2 & 2pq represent in this equation: 

p2 + 2pq + q2 = 1

  • p2 = frequency of homozygous dominant AA
  • q2 = 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.

q2 = 0.01

q = 0.1

p + 0.1 = 1

p = 0.9


What is the evidence from the table that non-agouti and blotched are alleles of different genes? (1)

 In Paris / London frequencies (of these alleles) add up to more than 1

e.g. 0.71 + 0.78 = 1.49

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