Biology PHall Red- Chapter 17 Evolution of Populations

Population

A group of individuals of the same species that live and breed together in a defined area.

Bell Curve

This graph plots the relative frequency of an observable polygenic trait or measurable variable.

Gene Pool

This term describes the total genetic information available in a population.

Allele Frequency

The number of times an allele appears in a population divided by the total number of times it could have appeared.

Hardy-Weinberg Principle

This principle states that allele frequencies will remain constant from generation to generation if 5 requirements are met.

Genetic Equilibrium

A situation in which allele frequencies remain constant within a population.

Immigration

This is the movement of individuals into a population.

Emigration

This is the movement of individuals out of a population.

Gene Flow

The process of genes moving from one population to another

Genetic Drift

This occurs when allele frequencies change in a population as a result of random events.

Sexual Selection

The tendency of one sex to select desirable traits in the other

Stabilizing Selection

This occurs when individuals with an average trait are at an advantage over individuals with extreme traits.

Directional Selection

This occurs when individuals with an extreme trait are at an advantage over those with the average trait or a trait at the other extreme.

Disruptive Selection

This occurs when individuals with the average trait are at a disadvantage compared to those individuals with traits at either extreme.

Speciation

This is the process of species formation.

Geographic Isolation

The physical separation of members of different populations.

Reproductive Isolation

This results from barriers to successful breeding between population groups in the same area.

Temporal Isolation

This results when the timing of important reproductive events separate two populations.

Behavioral Isolation

This results when certain activities of one species act as a barrier to reproduction with another population.

Polygenic Trait

A trait that is controlled by more than one gene is call a

Single-Gene Trait

A trait that is controlled by only one gene.

Phenotype

The physical appearance of an individual is known as its

Founder Effect

This occurs when a small number of individuals of a certain species are separated and form a new population.

Bottleneck Effect

The change in allele frequency following a dramatic reduction in the size of a population .

Species

A group of similar organisms that can breed and produce fertile offspring.

Molecular Clock

Model that uses DNA comparisons to estimate the length of time that two species have been evolving independently

Punctuated Equilibrium

Pattern of evolution in which long stable periods are interrupted by brief periods of more rapid change

Gradualism

The theory that evolution occurs slowly but steadily

Genotype

genetic makeup of an organism

Allopatric Speciation

The formation of new species in populations that are geographically isolated from one another.

Sympatric Speciation

Speciation without isolated populations.

Morphology

The scientific study of the internal and external structure and appearance of organisms.

Prezygotic Isolation

a barrier to successful breeding that occurs before fertilization, such as differences in mating time or behavior

Postzygotic Isolation

reproductive isolation that occurs after members of two different species have mated and produced a hybrid offspring. Such hybrids are usually unable to reproduce

Gene Shuffling

random shuffling of genes caused by sexual reproduction

Mutation

change in a DNA sequence that affects genetic information