Natural Selection

Natural Selection

The process where organisms better adapted to their environment tend to survive and produce more offspring.

Evolution

The change in the heritable characteristics of a population over time.

Genetic Variation

The difference in traits within a population that is essential for natural selection to occur.

Heritable Traits

Traits encoded in the nucleotide base sequence of genes in organisms that are passed to the next generation.

Paradigm

A distinct set of concepts and understandings, including theories, that defines a scientific discipline.

Phenotype

The observable traits of an organism, resulting from genotype and environmental factors.

Biotic Factors

Living factors that affect the survival of other organisms.

Abiotic Factors

Nonliving parts of an ecosystem that can affect the survival of organisms.

Overproduction of Offspring

The phenomenon where populations of species produce more offspring than can survive in an ecosystem.

Intraspecific Competition

Competition among individuals of the same species for resources such as food and shelter.

Stabilizing Selection

Occurs when the extreme phenotypes are selected against and the middle range of phenotypes are selected for.

Directional Selection

Occurs when one extreme of a range of phenotypes is advantageous to survival and reproduction.

Disruptive Selection

Occurs when individuals at the two extremes of the phenotypic range have advantages over individuals with intermediate phenotypes.

Gene Pool

All of the genes and their different alleles in an interbreeding population.

Hardy-Weinberg Equilibrium

Occurs when allele and genotype frequencies in a population remain constant from generation to generation.

Artificial Selection

Selective breeding carried out by humans to produce desirable traits in crop plants and domesticated animals.

Selection Pressure

Factors that affect the survival of an organism, making certain phenotypes more favorable.

Neo-Darwinism

The fusion of Darwin’s theory of natural selection with the principles of genetics.

Mutation

A change in the DNA sequence that can lead to genetic variation within a population.

Sexual Selection

Natural selection arising through preference by one sex for certain physical or behavioral traits in individuals of the other sex.

Hardy-Weinberg Equation

p² + 2pq + q² = 1, used to calculate the frequency of alleles and genotypes in a population under Hardy-Weinberg equilibrium.

p (allele frequency)

Represents the frequency of the dominant allele in a population in the Hardy-Weinberg equation.

q (allele frequency)

Represents the frequency of the recessive allele in a population in the Hardy-Weinberg equation.

Genotype Frequency

The proportion of different genotypes in a population calculated from allele frequencies.

Assumptions of Hardy-Weinberg

1. No mutations 2. Random mating 3. No natural selection 4. Large population size 5. No gene flow.

Applications of Hardy-Weinberg Principle

Used to determine whether a population is evolving by comparing observed genotypic frequencies to those expected under equilibrium.