D4.1 Natural Selection

Theory proposed by Charles Darwin

Natural Selection

natural selection

A process in which individuals with heritable traits that improve survivial and reproduction in a particular environment leave more offspring than others, causing allele frequencies in the gene pool to shift over generations

4 steps in Natural Selection

Variation, inheritance, overproduction, descent with modification

Lamarckism

Adapting during individuals' own lifetimes

Sources of genetic variation

Sexual reproduction, mutations, meiosis

Overproduction

The capacity of a species to produce more offsrping than the local environment or its carrying capacity can support

Abiotic

Non-living factor

Density-independent

Characteristics that are not affected by population density

Temperature

Density-independent factor

Density-dependent

Characteristics that vary depending on the population density

Intraspecific competition

Competition within a species

Evolutionary fitness

Takes into account the survival value and reproductive potential of a genotype

Example of evolutionary fitness

Giraffe ossicones

Selection pressure in sexual reproduction

The ability to mate

Sexual selection

When the sexes acquire distinct features because one sex is choosy

Intersexual selection

Males who compete for the right to mate with the females

Intrasexual selection

Males who compete for the right to mate with the females

John Endler

Evolutionary Biologist who studied Trinidadian guppies in the 1970s

Findings of Endler

Males tended to be more colorful, even though this does not allow easy camoflage

Gene pool

The total number of genes and alleles in a population, specifically among its reproducing members

Genetic equilibrium

Equal chance of contributing to the gene pool

Neo-Darwinism

Integration of understandings of natural selection and genetics

Evolution

Change in allele frequencies in a gene pool

Disruptive selection

The mean trait is selected against

Stabilizing selection

The mean trait is selected for

Directional selection

One extreme phenotype is selected for, and the other is selected against

Factor for directional selection

Change in the environment

Hardy-Weinberg Equilibrium

Model used to determine if the allel frequency in a population is changing or not therefore whether it is evolving

Conditions for Hardy-Weinberg

No mutations, random mating, no immigration, large population, no natural selection

Antibiotic resistance

Natural selection because humans are only inducing the pressure, but it isn't intended to happen