17.2.6
Hardy-Weinberg Principle
Using the Hardy-Weinberg Principle
Using the Hardy-Weinberg Principle
The Hardy-Weinberg principle is used to predict allele frequencies in a population. The principle is a mathematical model.


Predictions
Predictions
- The Hardy-Weinberg principle predicts that allele frequencies will not change from generation to generation.
- The allele frequencies do not change because a population’s allele and genotype frequencies are inherently stable.


Assumptions
Assumptions
- The Hardy-Weinberg principle only works if you make some assumptions about the population you are studying.
- The assumptions are:
- No mutations, migration or emigration.
- No selective pressure for or against a specific genotype.
- Population size is infinite.
- In real populations, these assumptions are not normally met but making assumptions is still useful because it provides a model we can compare to real population changes.
The Hardy-Weinberg Equation
The Hardy-Weinberg Equation
The Hardy-Weinberg equation is: p2 + 2pq + q2 = 1. The equation is used to predict the frequency of alleles, genotypes and phenotypes in a population.


p + q = 1
p + q = 1
- For every gene, there are two alleles present in an individual (except some genes on the X chromosome).
- If you know the frequency of one of these alleles, the equation p + q = 1 can be used to calculate the frequency of the other allele.
- p = frequency of one allele.
- q = frequency of other allele.


p2 + 2pq + q2 = 1
p2 + 2pq + q2 = 1
- The Hardy-Weinberg is equation: p2 + 2pq + q2 = 1
- p2 = pp = homozygous dominant.
- q2 = qq = homozygous recessive.
- 2pq = heterozygous.
- The components of the equation allows us to calculate the number of individuals in a population that have each genotype.


Predicting genotypes
Predicting genotypes
- By observing the phenotypes in a population, you can identify how many individuals carry the homozygous recessive allele genotype (q2).
- Only individuals who are homozygous recessive show the recessive phenotype.
- Individuals with the dominant phenotype could be homozygous dominant or heterozygous.
- This number can be used in the Hardy-Weinberg equation to allow the frequencies other two genotypes to be estimated.


Pea plants
Pea plants
- Pea plants can have yellow peas (pp or pq) or green peas (qq).
- If 0.25 of the population have green peas then q2 = 0.25.
- If q2 = 0.25, then q = 0.5.
- Using p + q = 1, p + 0.5 = 1, p = 0.5.
- 2pq = 0.50.
- p2 = 0.25.
- p = 0.5.
1Cell Structure
1.1Cell Structure
1.1.1Studying Cells - Microscopes
1.1.2Introduction to Eukaryotic & Prokaryotic Cells
1.1.3Ultrastructure of Eukaryotic Cells
1.1.4Ultrastructure of Eukaryotic Cells 2
1.1.5Ultrastructure of Eukaryotic Cells 3
1.1.6Prokaryotic Cells
1.1.7Viruses
1.1.8End of Topic Test - Cell Structure
1.1.9Exam-Style Question - Microscopes
1.1.10A-A* (AO2/3) - Cell Structure
2Biological Molecules
2.1Testing for Biological Modules
2.2Carbohydrates & Lipids
2.3Proteins
3Enzymes
4Cell Membranes & Transport
4.1Biological Membranes
5The Mitotic Cell Cycle
6Nucleic Acids & Protein Synthesis
6.1Nucleic Acids
7Transport in Plants
8Transport in Mammals
8.1Circulatory System
8.2Transport of Oxygen & Carbon Dioxide
9Gas Exchange
9.1Gas Exchange System
10Infectious Diseases
10.1Infectious Diseases
10.2Antibiotics
11Immunity
12Energy & Respiration (A2 Only)
13Photosynthesis (A2 Only)
14Homeostasis (A2 Only)
14.1Homeostasis
14.2The Kidney
14.3Cell Signalling
14.4Blood Glucose Concentration
14.5Homeostasis in Plants
15Control & Coordination (A2 Only)
15.1Control & Coordination in Mammals
15.1.1Neurones
15.1.2Receptors
15.1.3Taste
15.1.4Reflexes
15.1.5Action Potentials
15.1.6Saltatory Conduction
15.1.7Synapses
15.1.8Cholinergic Synnapses
15.1.9Neuromuscular Junction
15.1.10Skeletal Muscle
15.1.11Sliding Filament Theory Contraction
15.1.12Sliding Filament Theory Contraction 2
15.1.13Menstruation
15.1.14Contraceptive Pill
15.2Control & Co-Ordination in Plants
16Inherited Change (A2 Only)
16.1Passage of Information to Offspring
16.2Genes & Phenotype
17Selection & Evolution (A2 Only)
17.2Natural & Artificial Selection
18Classification & Conservation (A2 Only)
18.1Biodiversity
18.2Classification
19Genetic Technology (A2 Only)
19.1Manipulating Genomes
19.2Genetic Technology Applied to Medicine
19.3Genetically Modified Organisms in Agriculture
Jump to other topics
1Cell Structure
1.1Cell Structure
1.1.1Studying Cells - Microscopes
1.1.2Introduction to Eukaryotic & Prokaryotic Cells
1.1.3Ultrastructure of Eukaryotic Cells
1.1.4Ultrastructure of Eukaryotic Cells 2
1.1.5Ultrastructure of Eukaryotic Cells 3
1.1.6Prokaryotic Cells
1.1.7Viruses
1.1.8End of Topic Test - Cell Structure
1.1.9Exam-Style Question - Microscopes
1.1.10A-A* (AO2/3) - Cell Structure
2Biological Molecules
2.1Testing for Biological Modules
2.2Carbohydrates & Lipids
2.3Proteins
3Enzymes
4Cell Membranes & Transport
4.1Biological Membranes
5The Mitotic Cell Cycle
6Nucleic Acids & Protein Synthesis
6.1Nucleic Acids
7Transport in Plants
8Transport in Mammals
8.1Circulatory System
8.2Transport of Oxygen & Carbon Dioxide
9Gas Exchange
9.1Gas Exchange System
10Infectious Diseases
10.1Infectious Diseases
10.2Antibiotics
11Immunity
12Energy & Respiration (A2 Only)
13Photosynthesis (A2 Only)
14Homeostasis (A2 Only)
14.1Homeostasis
14.2The Kidney
14.3Cell Signalling
14.4Blood Glucose Concentration
14.5Homeostasis in Plants
15Control & Coordination (A2 Only)
15.1Control & Coordination in Mammals
15.1.1Neurones
15.1.2Receptors
15.1.3Taste
15.1.4Reflexes
15.1.5Action Potentials
15.1.6Saltatory Conduction
15.1.7Synapses
15.1.8Cholinergic Synnapses
15.1.9Neuromuscular Junction
15.1.10Skeletal Muscle
15.1.11Sliding Filament Theory Contraction
15.1.12Sliding Filament Theory Contraction 2
15.1.13Menstruation
15.1.14Contraceptive Pill
15.2Control & Co-Ordination in Plants
16Inherited Change (A2 Only)
16.1Passage of Information to Offspring
16.2Genes & Phenotype
17Selection & Evolution (A2 Only)
17.2Natural & Artificial Selection
18Classification & Conservation (A2 Only)
18.1Biodiversity
18.2Classification
19Genetic Technology (A2 Only)
19.1Manipulating Genomes
19.2Genetic Technology Applied to Medicine
19.3Genetically Modified Organisms in Agriculture
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