Evolution and Hardy Weinberg Principle: Definition, Steps and Examples

Evolution is a process of change. The species diversity evolved over many generations. The genetic variations are the key to evolution for changes. The natural selection given by Darwin stated that only the fittest individuals will survive and reproduce. This is the driving process of evolution over time. Adaptation and habitat improve the survival and reproduction of organisms. The theory of evolution is foundational.

This Story also Contains

1. What is the Hardy-Weinberg Principle?
2. Mechanisms of Evolution
3. Hardy-Weinberg Principle: Mathematical Model
4. Factors Affecting the Hardy-Weinberg Principle
5. Diagram: Representation Of the Hardy-Weinberg Principle
6. Recommended video for Hardy-Weinberg Principle
7. MCQs on Hardy-Weinberg Principle

The Hardy-Weinberg Principle explains gene stability. It predicts allele frequency in evolution. No evolution occurs under ideal conditions. Evolution happens if conditions are disturbed. It links genetics and evolution. Evolution, gene pool, and allele frequency change. The Hardy-Weinberg Principle supports evolutionary biology research.

What is the Hardy-Weinberg Principle?

The Hardy-Weinberg Principle explains the genetics of a population clearly under an ideal situation. It shows how the gene frequency stays constant in a population via the random mating process. The principle provides a mathematical model that helps in revealing evolution or no evolution. No evolution means genetic balance remains. This helps study genetic variation in populations. It defines when evolutionary forces are absent. These are exploration mechanisms of evolution here.

Mechanisms of Evolution

Mechanisms of evolution explain biological change. They include various factors and processes. It involves Charles Darwin's theory of natural selection. Small variations lead to adaptation and survival. Over time, changes cause new species. Darwin's theory focused on gradual evolution.

Gregor Mendel studied the genetic laws of inheritance patterns. His work showed that genetic variation arises naturally. Variation in genes drives evolutionary change. Later, Hugo de Vries proposed mutations.

Genetic mutations can change traits suddenly. This idea is called saltation theory. Saltation explains large, quick genetic shifts. It contrasts with Darwin’s gradual evolution. Both gradual and sudden changes occur. These mechanisms together drive biological evolution.

Hardy-Weinberg Principle: Mathematical Model

The Hardy-Weinberg Principle explains allele frequency stability. It shows how gene frequencies stay constant. This happens when evolutionary forces are absent. The population remains in genetic equilibrium. No mutation or selection means no evolution. The concept of Hardy-Weinberg thus provides a basis for understanding how population interaction occurs in evolution and which factors are responsible for driving them away from this equilibrium.

The equation representing the Hardy-Weinberg Equilibrium:

p² + 2pq + q² = 1

Here, p and q are allele frequencies.

p² = homozygous dominant,

2pq = heterozygous,

q² = homozygous recessive genotype frequency.

Factors Affecting the Hardy-Weinberg Principle

The Hardy-Weinberg Principle assumes genetic equilibrium. Certain factors disrupt this equilibrium state. These factors cause changes in allele frequency. Such changes lead to evolution in populations.

Diagram: Representation Of the Hardy-Weinberg Principle

The Hardy-Weinberg Principle represents a heterozygous parent (Aa), showing segregation of alleles into gametes with 50% probability for A and a alleles. This supports the Hardy-Weinberg equilibrium model, which assumes random mating and no evolutionary forces acting on the gene pool.

Recommended video for Hardy-Weinberg Principle

MCQs on Hardy-Weinberg Principle

Question: In a population of 1000 individuals, the frequency of the recessive allele for a particular trait is 0.2. What is the expected frequency of homozygous recessive individuals in the population, assuming Hardy-Weinberg equilibrium?

1. 0.04

2. 0.08

3. 0.16

4. 0.32

Answer: In a population under Hardy-Weinberg equilibrium, the genotype frequencies can be determined using the Hardy-Weinberg equation:

p² + 2pq + q² = 1,

Where:

p is the frequency of the dominant allele,
q is the frequency of the recessive allele, and
p², 2pq, and q² represent the frequencies of the three possible genotypes: homozygous dominant, heterozygous, and homozygous recessive, respectively.
Given that the frequency of the recessive allele (q) is 0.2, we can calculate the frequency of the dominant allele (p) as:

p = 1 - q = 1 - 0.2 = 0.8.

Using the Hardy-Weinberg equation, we can now calculate the expected frequency of homozygous recessive individuals (q²) as:

q² = (0.2)² = 0.04.

To obtain the expected count of homozygous recessive individuals in a population of 1000 individuals, we multiply the expected frequency (0.04) by the population size:

Expected count = q² * population size = 0.04 * 1000 = 40.

Therefore, the expected frequency of homozygous recessive individuals in the population is 40/1000 or 0.04.

Hence, option (a) is the correct answer.

Question: In the context of an irregular mating population, characterized by the presence of an autosomal recessive lethal gene with a frequency of 0.4, what would be the estimated frequency of carriers among a population consisting of 200 individuals?

1. 96

2. 36

3. 104

4. 72

Answer: In Hardy-Weinberg equilibrium,

p = frequency of the dominant allele

q = frequency of the recessive allele

In the question, it is given that q = 0.4

Applying Hardy-Weinberg equilibrium

p + q = 1

p = 1 - 0.4 = 0.6

Hence, the estimated frequency of carriers = 2pq = 2 x 0.4 x 0.6 = 0.48

Therefore, the estimated frequency of carriers in a population of 200 individuals with an autosomal recessive lethal gene frequency of 0.4 is: 0.48 x 200 = 96

Hence, the correct answer is option 1) 96

Question: The Hardy-Weinberg principle comes from considering what happens when Mendelian genes act in a population. The model predicts that there will be no change in allele frequencies when

1. Migration into the population occurs at a steady rate.

2. The population suffers a bottleneck.

3. A rare new mutation is associated with a sharp increase in fitness.

4. No evolutionary process is at work

Answer: The Hardy-Weinberg principle, derived from considering the effects of Mendelian genes in a population, predicts that there will be no change in allele frequencies when no evolutionary processes are at work. This assumption is based on the following conditions:

No mutations: The absence of new mutations ensures that there are no new alleles introduced into the population.

No migration: There is no migration into or out of the population, which would bring in or remove alleles.

Random mating: Individuals in the population mate randomly, without any preference for specific genotypes or alleles.

Large population size: The population size is large enough to prevent genetic drift, which is the random change in allele frequencies due to chance events in small populations.

No natural selection: There is no differential survival or reproductive advantage associated with specific genotypes. All genotypes have equal fitness and contribute equally to the next generation.

Under these assumptions, the Hardy-Weinberg principle predicts that the allele frequencies in a population will remain constant from generation to generation. This stable equilibrium is expressed by the Hardy-Weinberg equation, which relates the frequencies of alleles and genotypes in a population. Any deviation from the Hardy-Weinberg equilibrium indicates the presence of evolutionary processes such as mutation, migration, genetic drift, or natural selection.

Hence, the correct answer is option 4) No evolutionary process is at work.

Also Read:

• MCQs on Hardy-Weinberg Equilibrium

• Origin and Evolution of Man

• Adaptive Radiation