Shaping Evol. History Main Lecture

Population Genetics

Natural Selection and Mendel’s genetics combined

Population

Interbreedable groups of organisms from the same species

Gene pool

All available genes for a specific population

Variation

Different versions of an organism due to genes

Hardy-Weinberg Principle - Idealized Population

No mutations, No movements in or out of gene pool, probability through large population but no chance, mating is random, and all alleles are viable and all organisms reproduce

Hardy-Weinberg Principle - Effects of Multiple Alleles Formula

(p + q + r)² = 1

Hardy-Weinberg Principle - Genotype Formula

A² + 2Aa + a² = 1

Genetic Drift

Change in gene pool due to chance.

Genetic Drift and Evolution

Necessady for finding evolutionary course of population.

Founder Effect

A subset of a larger population living in a new environment may have over or under representation of alleles.

Population Bottleneck

Over or under representation of alleles in a population reduced in numbers independently of natural selection.

Gene Flow

Alleles moving in and out of a population.

Gene Flow and Natural Selection

Counteracts it

Natural Selection

The major force of evolution.

Natural Selection and Reproduction

Reproductive success results from interactions with environment and whole phenotype of organism.

Natural Selection and Gene Pools

Can change it for a population.

Natural Selection Constraints

Limited to gene variations available and physical genotype expressions

Degeneration

Loss of structures due to evolution

Stabilization Selection

Extremes selected against; narrowing variability

Directional Selection

One extreme is favored

Disruptive Selection

Average is selected against

Frequency Dependent

Decreases frequency of common phenotypes, increasing frequency of rarer ones.

Sexual Selection - Intrasexual

Competition within the same sex

Sexual Selection - Intersexual

Members of one sex select for traits of the other

Premating Isolating Mechanisms

Species develop mating rituals, and have species-specific auditory, visual, and chemical cure. Also temporally different

Postmating Isolating Mechanisms

Even if two different species mate, reproduction may fail, or offspring may die immediately, not mature, or mature but be sterile

Modes of Speciation - Allopatric

Geographically isolated species may be subject to different selective forces, leading to changes for a new species.

Modes of Speciation - Sympatric

Occurs without parent species isolation; instead due to changes in chromosome content of cells.

Rates of Evolution - Gradual

Occurs over long periods of time due to slow changes in selectives pressures

Rates of Evolution - Punctuated Equilibrum

Rapid initial change due to heavy selective pressures, followed by long periods of stability