Unit 7 Biology Test

Natural Selection key ideas

• Inherited variations

• Competition for resources

• Adaptation & fitness

• Survival & reproduction

Modes of Natural Selection

Stabilizing, Directional, Disruptive, Sexual

Stabilizing Selection

Average phenotype has higher fitness, becomes more common in population over time (graph goes toward mean)

Directional Selection

One extreme phenotype has higher fitness and becomes more common in population over time (graph toward extreme)

Disruptive Selection

Both extreme phenotypes have higher fitness and becomes more common over time (graph goes against the mean)

Sexual Selection

Males often have useless features to attract females. This can be harmful to their survival.

5 Mechanisms of Evolution

• Natural selection

• Gene flow (migration)

• Mutation

• Non random mating

• Genetic drift

Gene Flow

Transfer of alleles into or out of a population (migration)

Mutation

Leads to genetic variation because of new alleles. Can be harmful, neutral, or beneficial.

Non-Random Mating

When organisms are choosing their mate, certain traits may be selected for driving evolution of the species.

Genetic Drift

Chance events that cause a change in a allele frequencies. Most significant to small populations because they cause a loss of genetic variation.

Hardy Weinberg Equilibrium

Frequencies of alleles and genotypes in a population will remain constant from generation to generation (no evolution takes place). Must have no mutations, random mating, no natural selection, a large population, and no migration.

• p = dominant allele

• q = recessive allele

• p² = homozygous dominant (%)

• 2pq = heterozygous (%)

• q² = homozygous recessive (%)

Evolution

Complex change over time

3 types: Divergent, Convergent, Coevolution

Divergent Evolution

Develop different traits over time, different environment and pressures on survival.

Convergent Evolution

Develop similar traits over time, similar environment and pressures on survival.

Coevolution

Closely interacting species pressure one another (predator/prey).

Common Descent

All living things share a common ancestor at some point in history.

Decent with Modification

Each generation is slightly different than the previous because of mechanisms of evolution.

Evidence for Evolution

Homologous, Analogous, Vestigial structures

Homologous Structures

Similar structure and sometimes function. Have a common ancestor.

Analogous Structures

Similar function, but not structure. No common ancestor.

Vestigial Structures

Features that no longer seem to have a purpose. A leftover trait from an ancestor.

Embryo

Earliest stage of development. Similar features have similar DNA meaning they’re more closely related.

Speciation

Evolution can develop 2+ species from the same common ancestor

• Allopatric

• Sympatric

Allopatric Speciation

Physical barrier divides a population or a small group of separated from the main population.

Sympatric Speciation

New species evolved, while still inhabiting the same geographic region as its ancestor species.

Prezygotic Barriers

Prevent mating/fertilization, all ending up in different species being made

• Habitat isolation

• Temporal isolation

• Behavioral isolation

• Mechanical/ Anatomical isolation

• Gametic isolation

Habitat Isolation

Species live in different areas or habitats.

Temporal Isolation

Species breed at different times.

Behavioral Isolation

Unique behavioral patterns causing isolation.

Mechanical/Anatomical Isolation

Reproductive anatomy doesn’t fit with that of another species.

Gametic Isolation

Eggs & sperm can’t fuse because of proteins on gametes.

Postzygotic Barriers

Prevent hybrid zygote from developing into a normal adult

• Reduced hybrid viability

• Reduced hybrid fertility

• Hybrid breakdown

Reduced Hybrid Viability

Genes of different parent species may impair a hybrid’s development or survival.

Reduced Hybrid Fertility

Hybrid can develop into a healthy adult but cannot reproduce (sterile), usually because of different # of parents’ chromosomes.

Hybrid Breakdown

Hybrid of first generation could be fertile, but mating results in sterile offspring.

Punctuated Equilibrium

Rapid evolution after long stasis period followed by a period of no change (equilibrium).

Gradualism

When evolution occurs slowly over long time periods that add up over time to change environment.

Phylogenetic Trees

Diagrams representing evolutionary history of organisms that show the amount of change over time through fossils.

Cladograms

Show evolutionary relationships by comparing DNA and traits. Organisms are placed before characteristics it doesn't have and after characteristics it does.

Node

Point of intersection indicating most recent common ancestor between the two.

Clade

Group of organisms and their most recent common ancestor.

Outgroup

Lineage least closely related to the rest of the organism.

Ancestral trait

Shared by every organism except outgroup.

Derived traits

Shared by specific organisms, not all.