110 Hardy Weinberg Equilibrium

Summary

This video explains the concept of Hardy-Weinberg equilibrium and explores factors that can disrupt it using a case study of a population over a 60-year period. Initially in equilibrium in 1950, the population's genotype frequencies change by 2010, indicating that the population is no longer in equilibrium. The video delves into the five key factors that can disrupt Hardy-Weinberg equilibrium: mutation, non-random mating, gene flow, genetic drift, and natural selection. It also provides examples of genetic drift, including the bottleneck and founder effects, to illustrate how random events and isolated populations can influence allele frequencies.

Takeaways

• 😀 Hardy-Weinberg equilibrium describes a state where allele and genotype frequencies remain constant across generations in a large, randomly mating population.
• 😀 The equation for Hardy-Weinberg equilibrium is p² (AA) + 2pq (Aa) + q² (aa), where p is the frequency of the dominant allele and q is the frequency of the recessive allele.
• 😀 In the 1950 example, the population was in Hardy-Weinberg equilibrium with genotype frequencies matching the predicted values from the Hardy-Weinberg equation.
• 😀 By 2010, the allele and genotype frequencies in the population had shifted, indicating that the population was no longer in Hardy-Weinberg equilibrium.
• 😀 The shift in allele frequencies between 1950 and 2010 could be due to several evolutionary factors that disrupt equilibrium.
• 😀 The five factors that can violate Hardy-Weinberg equilibrium are mutation, non-random mating, gene flow, genetic drift, and natural selection.
• 😀 Mutation, though a potential cause of change in allele frequencies, is generally rare and doesn't have a significant short-term effect.
• 😀 Non-random mating, where individuals choose mates based on traits, can impact genotype frequencies but is often less influential than other factors.
• 😀 Gene flow, which involves the migration of individuals between populations, can introduce new alleles and alter allele frequencies in the population.
• 😀 Genetic drift is random chance that causes allele frequencies to fluctuate, with stronger effects in small populations. It can occur through the bottleneck effect or founder effect, where genetic diversity is reduced or altered by random events or small founder groups.

Q & A

What is Hardy-Weinberg equilibrium?

Hardy-Weinberg equilibrium is a principle in population genetics stating that allele and genotype frequencies in a population will remain constant over generations in the absence of evolutionary influences, provided certain conditions are met (no mutation, random mating, no gene flow, large population size, and no natural selection).

How did the population in 1950 demonstrate Hardy-Weinberg equilibrium?

In 1950, the genotype frequencies in the population (9 homozygous dominant, 42 heterozygous, 49 homozygous recessive) matched the predicted values from the Hardy-Weinberg equation, indicating that the population was in equilibrium at that time.

What is the significance of the Hardy-Weinberg equation in predicting allele frequencies?

The Hardy-Weinberg equation is used to predict the expected genotype frequencies in a population based on allele frequencies (p for the dominant allele and q for the recessive allele). This prediction can be compared to observed frequencies to determine if evolutionary forces are acting on the population.

What factors caused the population to deviate from Hardy-Weinberg equilibrium by 2010?

By 2010, the population had deviated from Hardy-Weinberg equilibrium due to factors like genetic drift, non-random mating, gene flow, and possibly natural selection. Changes in allele frequencies were evident when comparing observed genotype frequencies to the predicted frequencies.

What is genetic drift and how does it affect small populations?

Genetic drift refers to random fluctuations in allele frequencies due to chance events. It has a more significant effect in small populations because chance events can cause more drastic changes in allele frequencies compared to larger populations.

What is the bottleneck effect in genetic drift?

The bottleneck effect occurs when a population undergoes a drastic reduction in size due to an environmental event, such as a natural disaster. This results in a loss of genetic diversity, as the survivors may carry only a subset of the alleles from the original population.

Can you explain the founder effect in genetic drift?

The founder effect happens when a small group of individuals breaks off from a larger population to form a new population. The genetic makeup of the new population may differ significantly from the original population due to the limited genetic diversity of the founders.

What is the role of gene flow in affecting allele frequencies?

Gene flow refers to the movement of alleles between populations through immigration and emigration. This movement of individuals introduces new alleles into a population or removes alleles, altering the allele frequencies and potentially causing evolutionary changes.

How does natural selection influence allele frequencies?

Natural selection favors certain genotypes and phenotypes that are better suited for survival and reproduction in a given environment. This leads to changes in allele frequencies over time, as advantageous alleles become more common in the population.

What is the impact of mutations on allele frequencies?

Mutations can introduce new alleles into a population. However, mutations generally have a small impact on allele frequencies because they are relatively rare events. Over time, the frequency of new alleles may increase or decrease depending on other evolutionary factors like natural selection or genetic drift.