AP bio Unit 7

Evolution

Change in the genetic makeup of a population overtime

Natural Selection

Process by which organisms better suited to an environment have a higher chance of survival to reproduce

Variation

Genetic differences among organisms in a population

Adaptation

Factors that provides advantages in an environment

How do we measure evolutionary fitness?

By reproductive success

Fitness

The ability of an organism to survive and produce fertile offspring

Reproductive success

Production of offspring

Heritability

The ability to pass on traits

How does environmental stability affect evolution?

• More stable environments have populations that are less likely to evolve

• The more unstable an environment is, the quicker the evolution is

Why is genetic/phenotypic variation important to a population?

• Genetic variation increases the probability a population will survive in a changing environment

  • Genetic variation can result in varying phenotypes →higher chance of one being better suited

Genetic variation

Genotypic and Phenotypic differences between individuals in a population

Selective pressure

Any biotic or abiotic factors influencing survivability

How do phenotypes affect fitness?

Phenotypes that increase an individuals chances of survival will increase fitness

Artificial selection

The process by which humans select desirable traits in organisms and selectively breed those traits.

What can artificial selection result in?

• Phenotypes that wouldn’t exist in nature otherwise

• More OR less genetic diversity

Convergent evolution

The process by which similar environmental conditions select for similar traits in different populations/species overtime

Analagous structures

Similar traits observed in distantly related or unrelated species

Genetic drift

random change in frequency of a particular allele within a population

• nonselective, generally in small populations

Bottleneck

Large, diverse population suddenly reduced

• natural disasters

Founder effect

random, reduces genetic variation in a small population due to separation from a larger population

• migration/geological events

Gene flow

movement of individuals causes allele exchange between populations

• introduction of new genes →increased genetic variation

• Continued migration →decreases diversity

Hardy Weinberg model

a model describing and predicting allele frequencies in a non-evolving population

What conditions must be met for the Weinberg model?

• Large population →no genetic drift

• No migration → no gene flow

• No net mutation →No modified, deleted, or duplicated genes

• Random mating → no sexual selection

• Absence of selection → no natural selection

What is the equation for calculating genotype/phenotypes frequencies and what do the variables represent?

What is the equation for calculating the frequency of a particular allele and what do the variables represent?

Evidence supporting evolution

Geographical - evidence based on characteristics of a habitat or land

Geological - evidence based on features of the earth OVER TIME

• fossils document patterns of evolution and changes in environment

Physical - evidence based on phenotypes

Biochemical - evidence based on chemical composition

• comparison of biomolecules like DNA and proteins

Mathematical - evidence based on models/simulations that provide statistics

How can fossils be dated?

• age of surrounding rocks

• The decay of isotopes like carbon-14

• Geographical data

What do morphological homologies represent?

Features shared by common ancestry →modified traits shared by different species

Homologous structures

Variation in a structure that was present in a common ancestor (Divergent evolution)

Vestigial structures

Reduced or obsolete features that serve little to no purpose

Analagous structures

Structures that evolved independent of each other but in similar environments/selective pressures (white coats of animals in snowy environments) →convergent evolution

What evidence supports common ancestry for all eukaryotes?

• membrane bound organelles

• linear chromosomes

• Genes that contain introns

What are the similarities between mitochondria and chloroplasts?

• double membrane

• circular genomes

• ribosomes

• endosymbiotic theory - descirbe the processes and evidence supporting these similarities

What are chromosomal similarities between eukaryotic organisms?

• linear

• large genome

• capped with telomeres

• inside the nucleus

What does it mean when a pathogen is chemically compatible with the host?

• co-evolve with the host

• presence of pathogens can change phenotypes selected for and against

Phylogenetic tree

branched diagram showing the evolutionary relationship between species

• can show changes over time

Cladogram

a diagram used to show evolutionary relationships between species

• a clade is any group on a cladogram sharing a common ancestor

How is the out-group useful?

Provides a frame of reference.

Node

where 2 lines meet

• represents the most recent common ancestor

Root

represent the most common ancestor of all the species on the diagram

Derived characteristic

a trait in a recent species that evolved from an ancestor

Monophyletic

Diagram that includes an ancestor and ALL of its descendants

Paraphyletic

Diagram that includes an ancestor and SOME of its descendants

Polyphyletic

Diagram that includes descendants but no common ancestor

When does speciation occur?

When populations are reproductively isolated from each other.

Species

Group capable of interbreeding and exchanging genetic information to produce viable, fertile offspring.

Speciation

The creation of a new species

Prezygotic barriers

Prevent the formation of a fertilized egg

• habitat isolation: species occupy different habitats and rarely come into contact

• Temporal isolation: species breed at different times of the day, year, season

• Behavioral isolation: different courtship behaviors or preferences

• Mechanical isolation: structural differences in reproductive organs

• Gamete isolation: sperm and egg meet but do not produce a zygote

Postzygotic barriers

Prevent a zygote from developing into a viable, fertile offspring

• hybrid inviabilty: mating results in a zygote but incompatibility may prevent the development

• Hybrid sterility: an offspring is produced but is sterile

• Hybrid breakdown: hybrids are viable and sterile but resulting generations are feeble or sterile (decreasing fitness)

Allopathic speciation

Speciation due to a movement from one geographical region to another

• no gene flow

• Can expose populations to different selective pressures

Sympatric speciation

Speciation due to being reproductive isolated from a surviving ancestral population

• no geographical barrier

• Can result from genetic mutations

• Can result from habitat differences

• Can result from sexual selection

Punctuated equilibrium

Evolution occurs rapidly after a long period of stasis

• changing ecological conditions are the stimulus for evolution

Gradualism

Evolution occurs slowly

• ecological conditions change slowly

Adaptive radiation

The evolution of a new species that allows empty ecological roles/niches to be filled

Extinction

Disappearance of a species, such that no future generations will naturally populate the earth

What factors lead to extinction

Catastrophic changes to an ecosystem

How do environmental changes increase risk of extinction?

By changing conditions too rapidly for an organism to adapt.

How do speciation and extinction rates impact species diversity?

High speciation and low extinction rates can suit in high biodiversity. The opposite can result in low biodiversity.

How does extinction create new niches?

When a species goes extinct, the role that it played is open for another species to occupy.

• can lead to repod soeciation and adaptive radiation

How does genetic diversity of a species or population affect its ability to withstand environmental pressures?

Due to the diverse amount of adaptations, Higher genetic diversity results in an increased ability withstand environmental pressures and lower genetic diversity does the opposite.

Variation

Different combination of alleles and phenotypes in a population

What makes genetically diverse populations resilient?

Because of the diverse amount of adaptations in a genetically diverse populations, they are more likely to contain individuals that can withstand new environmental pressures.

Deleterious

Traits that reduce chance of survival

What determines if an allele is deleterious or adaptive?

The selective pressures of an environment

What scientific evidence provides support for models of the origin of life on earth?

Geological evidence

• earth formed apx 4.6 billion years ago

• The environment was too hostel for life until 3.9 billion years ago

• The earliest fossil evidence for life dates to 3.5 billion years ago

What did primitive earth provide

Inorganic precursors from which organic molecules could have been synthesized.

What was there a presence and absence of in primitive earth

Presence of free energy and an absence of significant quantity of atmospheric oxygen

What is RNA world hypothesis

Proposes that RNA could have been the earliest genetic molecule