Hardy–Weinberg Principle and Genetic Drift
Allele frequency equilibrium and the factors that disturb it. (Biology › Evolution, NEET UG syllabus.)
What is Hardy–Weinberg Principle and Genetic Drift?
A principle stating that allele and genotype frequencies in a population will remain constant from generation to generation in the absence of other evolutionary influences.
Key formula / rule: Hardy–Weinberg Allele Frequency
Key points
- State the Hardy–Weinberg Principle and its five conditions.
- Apply the Hardy–Weinberg equations to calculate allele and genotype frequencies.
- Explain the concept of genetic drift and its impact on allele frequencies.
- Differentiate between the Founder Effect and the Bottleneck Effect with examples.
Common exam trap
Confusing allele frequencies (p, q) with genotype frequencies (p², 2pq, q²).
Definitions
- Term
Hardy–Weinberg Principle
- Meaning
A principle stating that allele and genotype frequencies in a population will remain constant from generation to generation in the absence of other evolutionary influences.
- Term
Genetic Drift
- Meaning
A random change in the frequency of alleles in a population over generations, especially pronounced in small populations.
- Term
Allele Frequency
- Meaning
The proportion of a specific allele within a population's gene pool.
- Term
Genotype Frequency
- Meaning
The proportion of a specific genotype (combination of alleles) within a population.
- Term
Founder Effect
- Meaning
A type of genetic drift that occurs when a new population is established by a very small number of individuals from a larger population, leading to a gene pool that may not be representative of the original population.
- Term
Bottleneck Effect
- Meaning
A type of genetic drift that occurs when a population undergoes a drastic reduction in size due to a chance event (e.g., natural disaster), resulting in a smaller and less genetically diverse surviving population.
Learning objectives
State the Hardy–Weinberg Principle and its five conditions.
Apply the Hardy–Weinberg equations to calculate allele and genotype frequencies.
Explain the concept of genetic drift and its impact on allele frequencies.
Differentiate between the Founder Effect and the Bottleneck Effect with examples.
Identify factors that can disturb Hardy–Weinberg equilibrium and lead to evolution.
Formulae
- Name
Hardy–Weinberg Allele Frequency
- Note
Where 'p' is the frequency of the dominant allele and 'q' is the frequency of the recessive allele in a population.
- Expression
p + q = 1
- Name
Hardy–Weinberg Genotype Frequency
- Note
Where 'p²' is the frequency of the homozygous dominant genotype, '2pq' is the frequency of the heterozygous genotype, and 'q²' is the frequency of the homozygous recessive genotype.
- Expression
p² + 2pq + q² = 1
Prerequisites
Basic understanding of Mendelian genetics (alleles, genotypes, phenotypes).
Concept of a gene pool and population.
Basic probability and algebraic manipulation.
Common mistakes
Confusing allele frequencies (p, q) with genotype frequencies (p², 2pq, q²).
Assuming that a population in Hardy–Weinberg equilibrium is common in nature; it's a theoretical ideal.
Believing genetic drift is a form of natural selection; drift is random, selection is directional.
Underestimating the impact of population size on genetic drift; it's inversely proportional.
Incorrectly applying the Hardy–Weinberg equations, especially when calculating heterozygous frequency (2pq).
Keywords
Hardy–Weinberg
Genetic Drift
Allele Frequency
Genotype Frequency
Equilibrium
Evolution
Founder Effect
Bottleneck Effect
Gene Pool
Population Genetics
Practice preview
Which of the following is NOT a condition required for a population to be in Hardy-Weinberg equilibrium?…
easy
A small group of individuals from a large population migrates to a new, isolated island and establishes a new population. The allele frequencies in this new population are significantly different from the original mainla…
medium
In a population, if the frequency of allele 'A' (p) is 0.7, what is the frequency of allele 'a' (q)?…
easy