Eco 9_3 lecture

Charles Darwin and Gregor Mendel

• Charles Darwin is renowned for formulating the theory of natural selection, explaining how species evolve over time.
• Gregor Mendel, often referred to as the father of genetics, uncovered the basic laws of inheritance through his pea plant experiments.

Four Components of Darwin's Natural Selection

• Organisms generally produce offspring that resemble themselves.
• Variability exists among individuals, with some traits being heritable.
• More offspring are produced than the environment can support, leading to competition for resources.
• Individuals with beneficial traits enjoy greater survival rates and reproductive success.

Heritability

• Heritability is defined as the proportion of observable variation in a trait within a population that can be attributed to genetic differences among individuals.

Hardy-Weinberg Equilibrium

• Hardy-Weinberg Equilibrium (HWE) describes a theoretical situation where allele and genotype frequencies remain stable across generations, provided that no evolutionary influences act upon the population.

Allele and Genotype Frequencies under HWE

• Allele frequencies can be expressed as p + q = 1, where p represents the frequency of one allele and q represents the frequency of another.
• Genotype frequencies are represented by the equation p² + 2pq + q² = 1, depicting the proportions of homozygous and heterozygous individuals.

Assumptions of Hardy-Weinberg Equilibrium

• The population is assumed to be free from mutations that could alter allele frequencies.
• There is no migration (gene flow) into or out of the population.
• The population size must be large enough to prevent random fluctuations in allele frequencies (genetic drift).
• Mating within the population must be random without any biases.
• Natural selection must not influence reproductive success, allowing all individuals an equal opportunity to survive and reproduce.

Population Bottleneck vs. Founder Event

• A population bottleneck occurs when a significant reduction in population size results in decreased genetic variation due to the loss of many alleles.
• A founder event happens when a new population is established by a small group of individuals, who carry only a limited representation of the genetic variation from the larger population.

Types of Natural Selection on Phenotypes

• Directional Selection: This form of selection favors phenotypes at one extreme of the trait spectrum, driving the population’s traits in a specific direction.
• Stabilizing Selection: This type of selection favors the average or intermediate phenotypes, reducing variation within the population.
• Disruptive Selection: Here, selection acts against the average phenotype, favoring extremes, which can lead to the emergence of two or more distinct phenotypes within the population.

Key Requirement for Natural Selection

• Variation within populations is essential for natural selection to act, ensuring that different traits can be favored in changing environments.

Charles Darwin and Gregor Mendel

• Charles Darwin is renowned for formulating the theory of natural selection, explaining how species evolve over time.
• Gregor Mendel, often referred to as the father of genetics, uncovered the basic laws of inheritance through his pea plant experiments.

Four Components of Darwin's Natural Selection

• Organisms generally produce offspring that resemble themselves.
• Variability exists among individuals, with some traits being heritable.
• More offspring are produced than the environment can support, leading to competition for resources.
• Individuals with beneficial traits enjoy greater survival rates and reproductive success.

Heritability

• Heritability is defined as the proportion of observable variation in a trait within a population that can be attributed to genetic differences among individuals.

Hardy-Weinberg Equilibrium

• Hardy-Weinberg Equilibrium (HWE) describes a theoretical situation where allele and genotype frequencies remain stable across generations, provided that no evolutionary influences act upon the population.

Allele and Genotype Frequencies under HWE

• Allele frequencies can be expressed as p + q = 1, where p represents the frequency of one allele and q represents the frequency of another.
• Genotype frequencies are represented by the equation p² + 2pq + q² = 1, depicting the proportions of homozygous and heterozygous individuals.

Assumptions of Hardy-Weinberg Equilibrium

• The population is assumed to be free from mutations that could alter allele frequencies.
• There is no migration (gene flow) into or out of the population.
• The population size must be large enough to prevent random fluctuations in allele frequencies (genetic drift).
• Mating within the population must be random without any biases.
• Natural selection must not influence reproductive success, allowing all individuals an equal opportunity to survive and reproduce.

Population Bottleneck vs. Founder Event

• A population bottleneck occurs when a significant reduction in population size results in decreased genetic variation due to the loss of many alleles.
• A founder event happens when a new population is established by a small group of individuals, who carry only a limited representation of the genetic variation from the larger population.

Types of Natural Selection on Phenotypes

• Directional Selection: This form of selection favors phenotypes at one extreme of the trait spectrum, driving the population’s traits in a specific direction.
• Stabilizing Selection: This type of selection favors the average or intermediate phenotypes, reducing variation within the population.
• Disruptive Selection: Here, selection acts against the average phenotype, favoring extremes, which can lead to the emergence of two or more distinct phenotypes within the population.

Key Requirement for Natural Selection

• Variation within populations is essential for natural selection to act, ensuring that different traits can be favored in changing environments.

Explore the groundbreaking contributions of Charles Darwin and Gregor Mendel to biology in this quiz. Understand Darwin's natural selection theory and Mendel's principles of inheritance. Test your knowledge of these foundational figures and their work in genetics and evolution.