D4.1 Natural selection Notes

Natural Selection

The process where individuals with traits better suited to their environment have higher reproductive success, passing these traits to the next generation.

Overproduction of Offspring

Most species produce more offspring than the environment can support, leading to competition for resources.

Variation Among Individuals

Within a population, individuals vary in traits such as size, color, or speed, often due to genetic differences.

Struggle for Survival

Not all individuals survive to reproduce; those with advantageous traits are more likely to survive.

Differential Reproduction

Individuals with advantageous traits are more likely to reproduce and pass these traits to the next generation.

Change in Population Over Time

Over many generations, the population evolves as advantageous traits become more common.

Adaptation to the Environment

Traits that increase an organism's fitness are determined by environmental pressures.

Gradual vs. Rapid Evolution

Evolution can occur gradually but may happen rapidly in response to sudden environmental changes.

Paradigm Shift

A fundamental change in understanding; before Darwin, Lamarckism proposed traits could be acquired during a lifetime.

Darwin's Contribution

Darwin's theory explained that traits are inherited through genes, not acquired, leading populations to evolve over generations.

Fitness

How well an organism is adapted to its environment, influenced by its ability to survive and reproduce.

Variation

Differences in traits among individuals within a population, essential for natural selection.

Mutation

Changes in DNA sequences that create new alleles and expand the gene pool.

Meiosis

A process that increases genetic diversity by shuffling existing alleles and creating unique combinations.

Sexual Reproduction

Combines genetic material from two individuals, increasing variation among offspring.

Carrying Capacity

The maximum population size that an environment can sustain, dependent on limiting resources.

Density-Dependent Factors

Factors that intensify competition as population density increases.

Abiotic Factors

Non-living components of the environment that influence the survival and reproduction of organisms.

Biotic Factors

Living organisms that shape their environment, influencing natural selection.

Directional Selection

Favors one extreme phenotype, increasing the frequency of alleles associated with that trait.

Stabilizing Selection

Favors intermediate phenotypes, reducing variation in a population.

Disruptive Selection

Favors extreme phenotypes at both ends, potentially leading to population divergence.

Gene Pool

The total collection of all alleles in a population, changing through mutation, reproduction, and selection.

Allele Frequency

How common a particular allele is within a population, expressed as a proportion.

Genetic Drift

Random changes in allele frequencies, particularly pronounced in small populations.

Sexual Selection

A type of natural selection focused on mating success rather than survival.

Intraspecific Competition

Competition among individuals of the same species for limited resources.

Environmental Pressure

Factors that can affect survival and reproductive success, driving natural selection.

Heritability

The ability of a trait to be passed from parents to offspring through genetic information.

Epigenetics

Changes in gene expression that do not alter DNA sequences, potentially influenced by the environment.

Artificial Selection

The process by which humans select for specific traits in plants and animals to meet human needs.

Gene Flow

The transfer of alleles or genes from one population to another, which can alter allele frequencies.

Hardy-Weinberg Principle

A mathematical model predicting that allele and genotype frequencies remain constant unless evolutionary forces act on the population.

Hardy-Weinberg Equilibrium

A state in which allele frequencies remain constant across generations, requiring specific conditions to be met.

Mutations Do Not Occur

One of the conditions of Hardy-Weinberg equilibrium, meaning no new alleles are introduced.

Mating Is Completely Random

For Hardy-Weinberg equilibrium, individuals do not choose mates based on phenotype.

Population Size Is Large Enough

To prevent genetic drift, ensuring allele frequencies do not fluctuate randomly.

Natural Selection Does Not Favor Any Phenotype

All individuals have an equal chance of surviving and reproducing in a Hardy-Weinberg population.

Founder Effect

A phenomenon where a small group establishes a new population, often with different allele frequencies from the original population.

Feedback Mechanism

Processes that maintain homeostasis in organisms, can reflect principles seen in wider evolutionary concepts.

Guppy Populations

Used in studies to illustrate the effects of natural and sexual selection on traits over generations.

Biodiversity

The variety of life in the world or in a particular habitat, influenced by natural selection.

Survival of the Fittest

A phrase reflecting the process of natural selection where the best adapted organisms survive.

Camouflage

An adaptation that allows animals to blend into their environment to avoid predators.

Antibiotic Resistance

The ability of bacteria to resist the effects of medication previously effective against them, often due to artificial selection pressures.

Albinism

A genetic condition characterized by the absence of melanin, often used in Hardy-Weinberg examples.

Tay-Sachs Disease

A recessive genetic disorder used in demonstrating methods for calculating carrier frequencies.

Industrial Revolution Changes

Example showing how environmental changes can shift allele frequencies in populations.

Sexual Characteristics

Traits that evolve due to sexual selection, enhancing mating success over survival.

Population Genetics

The study of genetic variation within populations and the changes in allele frequencies.

SNP (Single Nucleotide Polymorphism)

A variation in a single nucleotide that occurs at a specific position in the genome.

Pike-Cichlid

A strong predator in Endler's guppy experiment, influencing natural selection.

Killifish

A weak predator in Endler's guppy experiment, balancing natural and sexual selection.

Adaptive Radiation

The rapid evolution of diversely adapted species from a common ancestor.

Speciation

The process by which new and distinct species evolve.

Genetic Markers

Specific sequences in the genome that can be used to trace inheritance and population dynamics.

Ethics in Genetics

Considerations surrounding human intervention in natural and artificial selection processes.

Conservation Genetics

The application of genetics to preserve species as well as their habitats.

Environmental Changes

Factors that can alter the balance of selection pressures on populations.