3.3.7 Allele Frequencies in Populations

Question 1

Define allele frequency

Answer 1

How frequently a particular allele appears in a population

Question 2

Define gene pool

Answer 2

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

Question 3

Define genetic bottlenecks

Answer 3

Event that causes big reduction in population

Question 4

Describe how genetic bottlenecks reduce genetic diversity

Answer 4

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

Question 5

Describe how selective breeding reduces genetic diversity

Answer 5

• 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

Question 6

What does the Hardy-Weinberg principle predict?

Answer 6

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

Question 7

Name 4 assumptions that the Hardy-Weinberg principle makes

Answer 7

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

Question 8

Name the 2 uses of the Hardy-Weinberg equations

Answer 8

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

Question 9

State the Hardy-Weinberg equation for predicting allele frequency

Answer 9

p + q = 1

Question 10

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

Answer 10

p² + 2pq + q² = 1

Question 11

State what p & q represent in this equation:

p + q = 1

Answer 11

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

Question 12

State what p², q² & 2pq represent in this equation:

p² + 2pq + q² = 1

Answer 12

• p² = frequency of homozygous dominant AA
• q² = frequency of homozygous recessive aa
• 2pq = frequency of heterozygous Aa/aA

Question 13

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.

Answer 13

Question 14

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.

Answer 14

Question 15

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.

Answer 15

q² = 0.01

q = 0.1

p + 0.1 = 1

p = 0.9

Question 16

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

Answer 16

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

e.g. 0.71 + 0.78 = 1.49