Chapter 12 - The Forces of Evolutionary Change

Evolution

• Explains the feature of all organisms from microbes to humans

• The genetic change over time

• Occurs when the heritable traits of a generation changes

Allele Frequencies

How common an allele is in a population

Allele Frequency Equation

# of copies of an allele / (Total # of alleles for the same gene in the population)

Gene Pool

The combination of all the genes (including alleles) present in a reproducing population or species

Uniformitarianism

Changes in nature are gradual

Hutton’s Theory

Catastrophism

Brief, violent events produce changes in nature

Cuvier’s Theory

Principle of superposition

This principle states that layers of rock are superimposed, or laid down one on top of another. The oldest rock strata will be on the bottom and the youngest at the top.

Natural Selection

• Animals with features best suited to the environment were able to survive and reproduce better than the others.

• The inherited characteristics of some individuals make them more likely to obtain resources, survive, and reproduce

Genetic Variation

Within a species, no two individuals (except identical siblings) are exactly alike. Some of this variation is heritable

Limited resources

Every habitat contains limited supplies of the resources required for survival.

Overproduction of offspring

More individuals are born than survive to reproduce.

Struggle for Existence

Individuals compete for the limited resources that enable them to survive.

Descent with modification

Over many generations, a population’s characteristics can change by natural selection, even giving rise to new species.

Artificial Selection

Also known as selective breeding.

Helped Darwin form the theory of evolution by natural selection.

Adaptations

Heritable features that provide a selective advantage because they improve an organism’s sability to survive and reproduce.

Ex. Dandelion’s bitter taste

Fitness

describes an organism’s genetic contribution to the next generation

Hardy-Weinberg Equilibrium

Is the unlikely situation in which allele frequencies do not change between generations.

When Hardy-Weinberg equilibrium Occurs

• No mutations

• The population is large enough to eliminate random changes in allele frequencies

• Individuals mate at random

• No migration

Modes of Natural Selection

• Directional

• Disruptive

• Stabilizing

Directional Natural Selection

Favors one phenotype over another

Disruptive Natural Selection

Favors extreme phenotypes

Stabilizing Natural Selection

favors intermediate phenotypes

Intrasexual selection

occurs in when the stronger individuals in a population battle to win access to mates. The weaker Individuals are denied access.

Genetic Drift

____________ is random sampling error. Allele frequencies can shift dramatically, and often become eliminated, when only part of a population survives to reproduce.

Founder Effect

When only a few individuals establish a new population, the allele frequency might change. This process illustrates the founder effect.

Population Bottleneck

A _________ occurs if a disaster drastically reduces the size of a population.

Gene flow

moves alleles between populations. This might affect the allele frequencies in both populations. Migration causes gene flow and ultimately reduces genetic differences between populations.

Nonrandom mating

Sexual selection and artificial selection can alter mating patterns in a population, preventing random mating.