Chapter 17 The Processes of Evolution

Population genetics

the study of evolution from a genetic point of view

Bell curve

curve that typically results when range of variation for a continuous trait is plotted against frequency in the population

Population

a group of individuals of the same species that interbreed.

Allele frequency

number of times allele occurs in gene pool divided by total number of alleles for that gene in the pool.

Phenotype frequency

the number of individuals with a particular phenotype divided by the total number of individuals in the population

Gene pool

all genes including all the different alleles that are present in a population.

Neutral mutation

a random change in the DNA of a gene that has no effect on survival or reproduction

Microevolution

change in allele frequencies in a population over generations.

Lethal mutation

a change in the DNA that causes the death of an organism

Genetic equilibrium

theoretical situation in which allele frequencies in a population remain the same

Hardy-Weinberg Equation

p2 + 2pq + q2 = 1 and p + q= 1

Hardy-Weinberg Equilibrium

shows that allele frequencies in a population tend to remain the same from generation to generation unless acted on by outside influences

Directional selection

form of natural selection in which the entire curve moves; occurs when individuals at one end of a distribution curve (extremes) have higher fitness than individuals in the middle (intermediate) or at the other end of the curve

Stabilizing selection

natural selection in which intermediate (average) phenotypes have a higher fitness more successfully than do extreme phenotypes

Disruptive selection

natural selection that favors individuals with either extreme of a trait; tends to eliminate intermediate phenotypes

Sexual dimorphism

differences in physical characteristics between males and females of the same species.

Sexual selection

a form of natural selection in which individuals with certain inherited characteristics are more likely than other individuals to obtain mates and pass on genes

Fitness

how well an organism can survive and pass on it's genes to offspring in its environment

Assortative mating

nonrandom mating in which individuals mate preferentially according to similar phenotypes

Balanced polymorphism

a situation in which two or more phenotypes (alleles) for a specific gene are at a high frequency in a population

Frequency-dependent selection

natural selection in which the fitness of a phenotype depends on how common the phenotype is in a population

Genetic drift

allele frequencies in a population change as a result of random events, or chance

Fixed

refers to an allele for which all members of a population are homozygous

Bottleneck effect

a change in allele frequency following a dramatic reduction in the size of a population, ex: overhunting of cheetahs

Founder effect

allele frequencies change as a result of the migration of a small subgroup of a population

Inbreeding

a selective breeding method in which two individuals with similar sets of alleles are crossed; mating among close relatives.

Gene flow

movement of genes from one population to another

Immigration

movement of individuals into an area occupied by an existing population

Emigration

the movement of individuals out of a population

Speciation

the formation of new species as a result of evolution

Biological species concept

the principle that defines a species as a group of organisms whose members can interbreed to produce offspring but cannot breed with other groups

Reproductive isolation

genetic separation of species that prevents them from interbreeding and producing fertile offspring

Prezygotic isolation

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

Postzygotic isolation

a barrier to successful breeding that occurs after fertilization, such as offspring not develop completely, die early, or may not be fertile

Geographic isolation

form of reproductive isolation in which members of populations are separated physically by geographic barriers such as rivers, mountains, or stretches of water

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Parapatric speciation

populations inhabiting different areas speciate while in contact along a common border, hybrids= death

Sympatric speciation

occurs when a species evolves into a new species in an area without a geographic barrier; polyploidy and sexual selection plays a role.

Stasis

condition in which there is no change in a population

Exaptation

evolutionary adaptation of an existing structure for a completely new purpose; dino feathers and bird feathers

Macroevolution

large-scale evolutionary changes that take place over long periods of time

Character

a heritable feature that varies among individuals

Derived trait

new feature that had not appeared in common ancestors

Clade

a group whose members share one or more defining derived traits

Monophyletic group

includes a single common ancestor and all of its descendants