Model Answer
0 min readIntroduction
The Hardy-Weinberg principle, formulated independently by G.H. Hardy and Wilhelm Weinberg in 1908, is a cornerstone of population genetics. It describes the conditions under which allele and genotype frequencies in a population will remain constant from generation to generation. This principle serves as a null hypothesis to test whether evolutionary forces are acting on a population. Understanding this law is crucial for comprehending the mechanisms of evolution and the factors that contribute to genetic variation within populations. The principle provides a baseline against which to measure evolutionary change.
Hardy-Weinberg Law of Genetic Equilibrium
The Hardy-Weinberg law states that in a large, randomly mating population, the allele and genotype frequencies will remain constant from generation to generation in the absence of certain evolutionary influences. This equilibrium is described by two equations:
- p + q = 1: Where 'p' represents the frequency of the dominant allele and 'q' represents the frequency of the recessive allele for a particular trait.
- p2 + 2pq + q2 = 1: Where p2 represents the frequency of the homozygous dominant genotype, 2pq represents the frequency of the heterozygous genotype, and q2 represents the frequency of the homozygous recessive genotype.
Assumptions of Hardy-Weinberg Equilibrium
For the Hardy-Weinberg law to hold true, several conditions must be met:
- No Mutation: The rate of mutation must be negligible.
- Random Mating: Individuals must mate randomly, without any preference for certain genotypes.
- No Gene Flow: There should be no migration of individuals into or out of the population.
- No Genetic Drift: The population must be large enough to avoid random fluctuations in allele frequencies.
- No Natural Selection: All genotypes must have equal survival and reproductive rates.
Limitations of the Hardy-Weinberg Law
The Hardy-Weinberg law is a theoretical model and rarely holds true in natural populations. Its limitations stem from the fact that the assumptions underlying the law are rarely fully met in real-world scenarios:
- Mutation: Mutation constantly introduces new alleles into the population, altering allele frequencies.
- Non-Random Mating: Assortative mating (preference for similar genotypes) and inbreeding can disrupt the equilibrium.
- Gene Flow: Migration can introduce or remove alleles, changing allele frequencies.
- Genetic Drift: In small populations, random chance events can significantly alter allele frequencies.
- Natural Selection: Differential survival and reproduction based on genotype directly affect allele frequencies.
Calculation of Allele Frequencies
Let's assume the blood group data represents a trait governed by two alleles, LM and LN. We'll assume the following genotype frequencies are observed in the population:
- LM LM: 49% (0.49)
- LM LN: 42% (0.42)
- LN LN: 9% (0.09)
Using the Hardy-Weinberg equations:
- Let p = frequency of LM allele
- Let q = frequency of LN allele
We know that p2 = 0.49, 2pq = 0.42, and q2 = 0.09
Therefore:
- p = √0.49 = 0.7
- q = √0.09 = 0.3
The frequency of the LM allele (p) is 0.7, and the frequency of the LN allele (q) is 0.3. We can verify this by checking if p + q = 1 (0.7 + 0.3 = 1), which it does.
Conclusion
The Hardy-Weinberg principle, despite its limitations, remains a fundamental concept in population genetics. It provides a valuable framework for understanding the factors that influence genetic variation and the mechanisms of evolution. While real populations rarely meet the ideal conditions for equilibrium, the principle serves as a crucial baseline for detecting and measuring evolutionary change. The ability to calculate allele frequencies based on genotype distributions, as demonstrated with the blood group data, highlights the practical application of this principle in population studies.
Answer Length
This is a comprehensive model answer for learning purposes and may exceed the word limit. In the exam, always adhere to the prescribed word count.