Population Genetics: Hardy-Weinberg Equilibrium

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Questions and Answers

What are three reasons as to why many natural populations do conform to the HWE?

Mutation and selection often negligible, molecular markers used in population genetics often neutral, migration and drift can cause deviations.

What are two deviations from HWE?

Selection acting on the marker, sampling bias.

What is the Wahlund effect and what are two possible causes of it?

A reduction in observed heterozygosity in a population due to subpopulation structure or null alleles.

What are three ways genetic diversity can be estimated?

Allelic Diversity (A), Polymorphic Loci (P), Observed Heterozygosity (Ho). Signup and view all the answers

What is the definition of 'expected heterozygosity' (He)?

Frequency of heterozygotes that would be expected if a population is in HWE. Signup and view all the answers

What are five influences on genetic diversity?

Genetic Drift, Population size, Population bottlenecks, Natural selection, Reproduction. Signup and view all the answers

What is the definition of genetic drift?

Change in allele frequencies over time due to random events. Signup and view all the answers

What are three causes of genetic drift?

Drift in chronically small populations, genetic bottlenecks, founder effect. Signup and view all the answers

What is the definition of the founder effect?

When small populations colonize a new area, the individuals are unlikely to have the same allele frequencies as the parent's gene pool. Signup and view all the answers

What is the definition of a census population size?

The number of individuals within a population. Signup and view all the answers

What is the definition of an effective population size?

Theoretical size of an ideal population where genetic diversity can be maintained. Signup and view all the answers

What are three factors that can contribute to a reduced effective population size?

Unequal sex ratios, variation in reproductive success, fluctuating census population size. Signup and view all the answers

What is the definition of a population bottleneck and what are two ways it can decrease effective population sizes?

Population having an abrupt contraction in numbers; it decreases effective population size by changing gene frequencies and causing a decline in genetic variation. Signup and view all the answers

What are the three types of natural selection with explanations?

Stabilising selection: selects against extreme phenotypes, directional selection: favours higher or lower values of a characteristic, disruptive selection: two or more phenotypes are selected. Signup and view all the answers

What is the definition of inbreeding?

Occurs when individuals mate with close relatives, increasing the proportion of homozygotes but not altering allele frequencies. Signup and view all the answers

Study Notes

Hardy-Weinberg Equilibrium (HWE) Compliance

Many natural populations deviate from HWE due to factors like mutation and selection being generally negligible.
Neutral molecular markers (e.g., microsatellites, introns) often used in population genetics exhibit minimal selection pressure.
Migration and genetic drift can significantly influence allele frequencies, causing deviations.

Deviations from HWE

Selection can directly influence specific markers, skewing results.
Sampling bias, particularly from small sample sizes, may distort allele frequency estimates.

Wahlund Effect

Characterized by reduced heterozygosity in a population, resulting in a higher than expected proportion of homozygotes under HWE.
May arise from subpopulation structure (where different genetic groups are not sampled equally).
Null alleles in microsatellite analyses can also contribute to this effect.

Estimating Genetic Diversity

Allelic Diversity (A): Measures the number of alleles present in a population.
Polymorphic Loci (P): Counts loci that have at least two alleles.
Observed Heterozygosity (Ho): Proportion of heterozygotes observed in the population.

Expected Heterozygosity (He)

Represents the frequency of heterozygotes anticipated in a population under HWE conditions.

Influences on Genetic Diversity

Genetic drift can cause random changes in allele frequencies.
Size of the population affects the potential for genetic variation.
Population bottlenecks can drastically reduce genetic variation.
Natural selection can promote or diminish genetic diversity based on environmental pressures.
Patterns of reproduction influence genetic outcomes within a population.

Genetic Drift

Defined as random fluctuations in allele frequencies over time, particularly evident in small populations.
Can result in the loss of genetic variation and fixation or complete loss of certain alleles.

Causes of Genetic Drift

Commonly occurs in small or chronically declining populations.
Genetic bottlenecks can lead to sudden decreases in genetic diversity.
The founder effect emerges when new populations originate from a small, unrepresentative sample of a larger population.

Founder Effect

Occurs when a new population is established by a small group, leading to potential differences in allele frequencies compared to the original population.

Census Population Size

Refers to the total number of individuals in a population at any given time.

Effective Population Size

Theoretical concept representing the size of an ideal population in which genetic diversity is maintained.
Indicates the rate at which genetic diversity may diminish due to genetic drift.

Factors Reducing Effective Population Size

Unequal sex ratios can lead to reduced genetic diversity.
Variation in reproductive success impacts genetic contribution to the next generation.
Fluctuations in census size can distort effective population estimates.

Population Bottleneck

A significant and rapid decrease in population numbers.
Reduces effective population size through altered gene frequencies and loss of genetic variability.

Types of Natural Selection

Stabilizing Selection: Favors intermediate phenotypes, reducing extremes.
Directional Selection: Selects for a Phenotype at one end of the spectrum, changing population traits over time.
Disruptive Selection: Encourages multiple distinct phenotypes within the same population.

Inbreeding

Defined as mating among close relatives, affecting the genetic structure without changing allele frequencies.
Leads to an increased proportion of homozygotes across all loci, influencing genetic health.

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Description

This quiz explores the Hardy-Weinberg Equilibrium (HWE) and its compliance in natural populations. It covers factors influencing deviations from HWE, the Wahlund effect, and methods for estimating genetic diversity. Test your understanding of these key concepts in population genetics!