D4.1 (Natural Selection)

Evolution

Change in the allele frequencies of a population over successive generations.

Natural Selection

The process in which individuals with advantageous heritable traits survive and reproduce more successfully. varsitytutors+1

Biodiversity

The variety of life at genetic, species and ecosystem levels.

Paradigm

A widely accepted model or framework used to understand a subject.

Paradigm Shift

A major change in the accepted way of understanding or explaining a subject.

Mutation

A random change in the DNA base sequence that can create a new allele.

Sexual Reproduction

Reproduction involving the fusion of gametes from two parents, producing genetically varied offspring.

Variation

Differences in characteristics between individuals of the same species.

Genetic Variation

Differences in DNA or alleles among individuals in a population.

Allele

A specific version of a gene.

Gene

A heritable length of DNA that codes for a functional product or characteristic.

Meiosis

Nuclear division that produces four genetically different haploid cells from one diploid cell.

Crossing Over

Exchange of corresponding sections of DNA between homologous chromosomes during meiosis.

Independent Assortment

The random distribution of homologous chromosome pairs into gametes during meiosis.

Gametes

Haploid reproductive cells, such as sperm and egg cells, that fuse during sexual reproduction.

Carrying Capacity

The maximum population size that an environment can sustainably support.

Competition

The struggle between organisms for limited resources.

Biotic Factors

Living components of an ecosystem that affect organisms.

Abiotic Factors

Non-living physical or chemical components of an ecosystem that affect organisms.

Selection Pressure

An environmental factor that affects the survival and reproduction of individuals with different traits.

Phenotype

The observable characteristics of an organism, produced by its genotype and environment.

Genotype

The allele combination possessed by an organism.

Density-Independent Factors

Environmental factors whose effects do not depend on population density, such as floods or droughts.

Intraspecific Competition

Competition between individuals of the same species.

Sexual Selection

Selection caused by differences in an organism’s ability to attract mates or compete for mating opportunities.

Gene Pool

All the genes and their alleles present in an interbreeding population.

Reproductive Isolation

The prevention of gene flow between populations because they cannot produce fertile offspring together.

Geographical Isolation

The separation of populations by physical barriers, preventing interbreeding and gene flow.

Neo-Darwinism

The modern theory of evolution combining natural selection with Mendelian genetics and mutation.

Genetics

The study of genes, inheritance and variation in organisms.

Stabilising Selection

Selection that favours intermediate phenotypes and acts against both extremes.

Directional Selection

Selection that favours one extreme phenotype, shifting the population’s characteristics in one direction.

Disruptive Selection

Selection that favours both extreme phenotypes over the intermediate phenotype.

Hardy-Weinberg Equation

The equations p+q=1p+q=1p+q=1 and p2+2pq+q2=1p^2+2pq+q^2=1p2+2pq+q2=1, used to calculate allele and genotype frequencies.

Hardy-Weinberg Principle

The principle that allele and genotype frequencies remain constant when no evolutionary forces act on a population.

Artificial Selection

The human-directed selection and breeding of organisms with desired characteristics.

Selective Breeding

The deliberate mating of organisms with desirable traits to increase the frequency of those traits in offspring.