AP Biology: Unit 7 Natural Selection (Chapters 19~22) - Majoros

Speciation

The origin of new species

Macroevolution

Broad patterns of evolutionary change above the species level

Biological Species Concept

A group of populations whose members have the potential to interbreed in nature and produce viable,

fertile offspring

Reproductive isolation

Barriers impede two species from producing viable, fertile offspring

Hybrids

Offspring of crosses between different species

Prezygotic Barriers

Before sperm fertilizes egg

Habitat isolation

Two species encounter each other rarely, or not at all, because they occupy different habitats, even though not isolated by physical barriers

Temporal isolation

Species that breed at different times of the day, different seasons, or different years cannot mix their gametes

Behavioral isolation

Courtship rituals and other behaviors unique to a species are effective barriers

Mechanical isolation

Morphological differences can prevent successful mating

Gametic Isolation

Sperm of one species may not be able to fertilize eggs of another species

Postzygotic barriers

Inviability of offspring created after fertilization

Reduced hybrid viability

Fertilized eggs fail to develop

Reduced hybrid fertility

Even if hybrids are vigorous, they may be sterile

Hybrid breakdown

Some first-generation hybrids are fertile, but when they mate with another species or with either parent species, offspring of the next generation are feeble or sterile

Morphological Species Concept

Defines a species by structural features

Ecological Species Concept

Views a species in terms of its ecological niche

Phylogenetic species concept

Defines a species as the smallest group of individuals on a phylogenetic tree

Allopatric Speciation

Physical barrier separates a population; form of speciation

Sympatric Speciation

No barrier separates a population; form of speciation

Polyploidy

Possessing more than 2 sets of chromosomes; occurs most often in plants and decreases gene flow between polyploids and normal individuals

Punctuated Equilibrium

Periods of apparent stasis interrupted by sudden change; supported by fossil evidence

Gradualism

Slow, steady change of organisms to new species

population

The evolutionary impact of natural selection is only apparent in the changes in a _______ over time

microevolution

a change in allele frequencies in a population over generations

genetic variation

differences among individuals in the composition of their genes or other DNA segments

sources for genetic variation

-formation of new alleles

-altering gene number or position

-rapid reproduction

-sexual reproduction

mutation

a change in the nucleotide sequence of an organism's DNA

population

a group of individuals of the same species that live in the same area and interbreed, producing fertile offspring

gene pool

consists of all copies of every type of allele at every locus in all members of the population

p

the frequency of the C^R allele in the gene pool of this population

q

the frequency of the C^W allele in the gene pool of this population

Hardy-Weinberg Principle

this principle states that the frequencies of alleles and genotypes in a population will remain constant from generation to generation, provided that only Mendelian segregation and recombination of alleles are at work

Equilibrium

a gene pool is in Hardy-Weinberg _____

Hardy Weinberg proportion

p^2 + 2pq + q^2 = 1

Conditions for Hardy Weinberg Equilibrium

1. No mutations

2. Random mating

3. No natural selection

4. Extremely large population size

5. No gene flow

adaptive evolution

evolution that results in a better match between organisms and their environment

genetic drift

A change in the allele frequency of a population as a result of chance events rather than natural selection

founder effect

when a few individuals become isolated from a larger population, this smaller group may establish a new population whose gene pool differs from the source population

bottleneck effect

Genetic drift resulting from the reduction of a population, typically by a natural disaster, such that the surviving population is no longer genetically representative of the original population

Significant points about Genetic Drift

1. Genetic drift is significant in small populations

2. Genetic drift can cause allele frequencies to change at random

3. Genetic drift can lead to a loss of genetic variation within populations

4. Genetic drift can cause harmful alleles to become fixed

gene flow

the transfer of alleles into or out of a population due to the movement of fertile individuals or their gametes

natural selection

_____ is not random, and consistently increases the frequencies of alleles that provide reproductive advantage and thus leads to adaptive evolution

sexual dimorphism

a difference between the two sexes in secondary sexual characteristics

ex: diff in size, color, ornamentation, and behavior

heterozygote advantage

Greater reproductive success of heterozygous individuals compared to homozygotes; tends to preserve variation in gene pools

defined in terms of genotype NOT phenotype

adaptation

Inherited characteristic of an organism that enhances its survival and reproduction in a specific environment.

analogous

Having characteristics that are similar because of convergent evolution, not homology.

artificial selection

The selective breeding of domesticated plants and animals to encourage the occurrence of desirable traits.

biogeography

The scientific study of the past and present geographic distributions of species

convergent evolution

The evolution of similar features in independent evolutionary lineages.

evolution

Descent with modification; the idea that living species are descendants of ancestral species that were different from the present-day ones; also defined more narrowly as the change in the genetic composition of a population from generation to generation.

evolutionary tree

A branching diagram that reflects a hypothesis about evolutionary relationships among groups of organisms.

fossil

A preserved remnant or impression of an organism that lived in the past.

homologous structures

Structures in different species that are similar because of common ancestry.

homology

Similarity in characteristics resulting from a shared ancestry.

natural selection

A process in which individuals that have certain inherited traits tend to survive and reproduce at higher rates than other individuals because of those traits.

Pangaea

The supercontinent that formed near the end of the Paleozoic era, when plate movements brought all the landmasses of Earth together.

vestigial structure

A feature of an organism that is a historical remnant of a structure that served a function in the organism's ancestors.

Phylogeny

The evolutionary history of a species or group of species.

Taxonomy

How organisms are named and classified

Binomial

Two-part format of the scientific name that was instituted in the 18th century by Carolus Linnaeus

Genus

Group to which the species belongs, also the first part of a binomial

Taxon

a named taxonomic unit at any given level in the hierarchy

Phylogenetic tree

A branching diagram representing the evolutionary history of a group of organisms

Branch point

Represents the common ancestor of the two evolutionary lineages diverging from it

Sister taxa

Groups of organisms that share an immediate common ancestor that is not shared by any other group

Rooted

A branch point within the phylogenetic tree represents the most recent common ancestor of all taxa in the tree

Homologies

phenotypic and genetic similarities due to shared ancestry

Analogy

similarity between organisms that is due to convergent evolution

Clades

Groups which include an ancestral species and all of its descendants

Monophyletic

Consists of an ancestral species and all of its descendants

Paraphyletic

Group which consists of an ancestral species and some, but not all, of its descendants

Polyphyletic

Group which includes distantly related species but does not include the most recent common ancestor

Shared ancestral character

A character that originated in an ancestor of the taxon

Outgroup

a species or group of species from an evolutionary lineage that is closely related to but not part of the group of species we are studying

Maximum parsimony

We should first investigate the simplest explanation that is consistent with the facts