Unit 7: Natural Selection Flashcards
Several examples of evidence for evolution from different scientific disciplines and how each supports change in populations over time
- Sticklebacks & having a pelvic spine
- Finches long beak vs small beak - had unique beak shapes adapted to the food sources available in their specific habitat
- Rock pocket mice - on dark volcanic rock = darker mice, lighter sand colored mice
Homologous structures
structures similar anatomy from common ancestors (eg. forelimbs of human/cat/whale/bat) but differ in function
Analogous structures
various structures in different species have same function but have evolved separately, do not share common ancestor (bug wings vs bird wings) + do not necessarily have same structures
How do Homologous and Analogous structures relate to evolution?
Noting the structures of these organisms help understand whether they share a common ancestor
Main ideas of Natural Selection
Evolution is change in species over time.
There is overproduction of offspring, which leads to competition for resources.
Heritable variations exist within a population.
These variations can result in differential reproductive success.
Over generations, this can result in changes in the genetic composition of the population.
Main ideas of Natural Selection
2
Competition for limited resources results in differential survival
Evolutionary Fitness: Individuals w/ more favorable adaptations are more likely to survive & produce more offspring, & pass on traits
If environ changes or individuals move to new environ, new adaptations & new species may arise.
Populations evolve, not individuals.
Evidence for Evolution:
1. Direct Observations
Examples: Insect populations become resistant to pesticides (DDT)
Antibiotic-resistant bacteria (MRSA)
Peppered moth (pollution in city vs. country)
Evidence for Evolution:
2. Homology
Characteristics in related species can have underlying similarity even though functions may differ
Embryonic homologies
Similar early development (eg. vertebrate embryos with tail & pharyngeal pouches) (DISCREDITED)
Vestigial organs
Structures w/little or no use (eg. flightless bird wings)
Molecular homologies
Similar DNA and amino acid
sequences
Evidence for Evolution:
3. Fossil Record
Fossils found in sedimentary rock
Show evolutionary changes that occur over time & origin of major new groups
Transitional forms = links to modern species
Evidence for Evolution:
4. Biogeography
Geographic distribution of a species
Species in nearby geographic areas resemble each other
Continental drift & Pangaea explains similarities on different continents
Endemic species: found at a certain geographic location & nowhere else
Ex: Marine iguanas in the Galapagos
Adaptations
Enhance an organism’s ability to survive & reproduce in specific environments (fitted to environ)
Ex: Desert fox - large ears, arctic fox - small ears
Variations
Any diff between cells, individual organisms, or organsims groups of any species caused by genetic diff or by effect of environmental factors on the expression of the genetic potentials
Time effect on Evolution
Can’t evolve in one generation
Reproductive success
Passing of fittest genes onto next generation so they can pass those genes on (tally of offspring produced by an individual)
Heritability
Amount of phenotypic (observable) variation in a population that is attributable to individual genetic differences
What are the only source of new genes and new alleles?
Mutations:
The three ways in which sexual reproduction
produces genetic variation.
The conditions for Hardy-Weinberg equilibrium.
How to use the Hardy-Weinberg equation to
calculate allele frequencies to test whether a
population is evolving.
What effects genetic drift, migration, or selection
may have on a population, and analyze data to
justify your predictions.
Microevolution
Evolution on smallest scale
Change in allele frequencies in a population over generations
Sources of Genetic variation
Mutations
Fast Reproduction
Sexual Reproduction
Mutations
Only source of new alleles & new genes
Mutations in gametes passed to offspring
Point mutations
Chromosomal mutations → gene duplication
Sexual Reproduction
shuffle existing alleles
1. Crossing over
2. Independent assortment
3. Random Fertilization
Conditions for Hardy-Weinberg Equilibrium
No mutations (no new alleles in gene pool)
Random mating. (no sexual selection)
No natural selection.
Extremely large population size. (no genetic drift- change in frequency of an existing gene variant in the population due to random chance)
No gene flow. (no emigration, immigration - movement in or out of the population or reproductive contact with other populations)
If any of the conditions for the Hardy-Weinberg Equilibrium are NOT met…?
Microevolution is occurring
Hardy-Weinberg Equation
p = dominant allele
q = recessive allele
p+q=1
homozyg. dominant = p^2
homozygous recessive = q^2
hetero. = 2pq
Genetic Drift
Changes in gene/allele frequencies from generation to generation as a result of random processes
Effect: changes gene frequencies (increases or decreases genetic diversity)
Significant genetic drift in small populations
2 types of genetic drift
Founder Effect
Bottleneck Effect
Bottleneck Effect
Severe drop in population size
Certain alleles may be over/under represented
Founder Effect
few individuals become
isolated from larger population → certain alleles over/under represented
Gene Flow
population gains/loses alleles
due to immigration or emigration
Migration effect on pop
changes # of species in a population + what genes are present
Natural Selection effect on pop
genes in a pop will adjust to become more favorable/fitt for the current environment (sexual/natural)
Natural selection can occur in 3 ways:
Directional Selection
Disruptive Selection
Stabilizing Selection
Directional selection
beak size of birds increase/decrease during wet/dry seasons
Disruptive selection
want to be either rock pocket mice or sand pocket mice
Stabilizing selection
Want to be very mid: average human birth weight
Intrasexual selection:
competition within same sex
Intersexual selection:
mate choice
Taxonomic categories
Kingdom, Phylum, Class, Order, Family, Genus, Species. Domain (Archaea, bacteria, Eukarya) is the biggest. The further into the tree you go, the closer the organisms are to each other.
Ordered division of organisms
based on similar/different
characteristics
Dear King Philip Came Over
For Good Soda
Each category at any level is
called a taxon.
Systematics used to develop phylogenetic trees
Using fossils, morphology (homologous structures), & molecular evidence (DNA/amino acids), one creates a tree, placing the most closely related organisms together.
Phylogenetic Tree
Branching diagram that shows evolutionary history of a group of organisms
Each branch = closer hallway to other species, can represent genetic change or time (common ancestor),
3 Domains of Life (similarities & differences)
Eukarya: Eukaryotes, have a nucleus, membrane bound organelles, introns, histone proteins associated with DNA, but have a linear chromosome.
Archaea: don’t have a nuclear membrane, don’t have membrane bound organelles, do have introns, do have histone proteins associated w/ DNA, and do have a circular chromosome
Bacteria: share same traits as Archaea but don’t have introns or histone proteins associated w/ DNA
Elements conserved across all 3 domains
DNA and RNA are carriers of genetic info
Universal genetic code (codons → amino acids)
Conserved metabolic pathways
Conserved elements in Eukaryotes
Cytoskeleton
Membrane-bound organelles
Linear chromosomes
Endomembrane systems (including nuclear envelope)
what is the significance of widely conserved processes across the three domains of life?
If a gene is widely conserved = crucial to species’s survival.
Gene = similar across organisms of all domains
Divergent Evolution
when individuals in one species, or closely related species, acquire enough variations in their traits that it leads to two distinct new specie (one common ancestor)
Convergent Evolution
two unrelated species develop similar traits because they live in similar environments. (no common ancestor)
Cladogram
Clade = group of species that includes an ancestral
species + all descendents
Shared derived characteristics (evolutionary novelties) are used to construct cladograms ex: hair
Horizontal Gene Transfer
Movement of genes between different domains
Exchange of transposable elements, plasmids, viral infections, fusion of organisms
Speciation may occur when two populations become
reproductively isolated from each other.
There are prezygotic and postzygotic barriers that maintain
reproductive isolation in natural populations.
How allopatric and sympatric speciation are similar and different.
How a change in chromosome number can lead to sympatric
speciation.
Why speciation rates are often rapid in situations where adaptive
radiation occurs or during times of ecological stress.
The connection between speciation in a isolated population and a
change in gene frequency, a change in the environment, natural
selection, and/or genetic drift.
How punctuated equilibrium and gradualism describe two
different tempos of speciation.
Species
pop or group of pops: members have the potential to interbreed in nature & produce viable,fertile offspring (can make more babies) Reproductively compatible
Reproductive isolation
barriers that prevent members of 2
species from producing viable, fertile hybrids
Prezygotic Barriers
Prevent mating or hinder fertilization
Types: Habitat isolation, Temporal isolation, Behavioral isolation, Mechanical isolation, Gametic isolation
Postzygotic Barriers
Prevent hybrid zygote from developing into fertile adult
Types: Reduced hybrid viability, Reduced hybrid fertility, Hybrid breakdown
can speciation occur when two populations become reproductively isolated from each other?
yes
Allopatric Speciation
Geographically isolated
pops (physical barrier), Caused by geologic events or processes -> evolve diff species
Evolves by natural selection & genetic drift
shares common ancestor
Ex: Squirrels on N/S rims of
Grand Canyon
Sympatric Speciation
Overlapping populations w/ in same geographic area -> just randomly evolves into separate species w/o geographical separation
shares common ancestor
Gene flow between subpops blocked by: polyploidy, habitat differentiation, sexual selection
Ex: polyploidy in 80% of plants
(oats, cotton, potatoes, wheat)
Autopolyploid (Sympatric speciation thru diff chromosome numbes)
extra sets of chromosomes
Failure of cell division (2n → 4n)
Ex: Strawberries are 4n, 6n, 8n,
10n (decaploid)!
Allopolyploid (Sympatric speciation thru diff chromosome numbes)
2 species produce a hybrid
Species A (2n=6) + Species B (2n=4) → Hybrid (2n=10)
How does polyploidy cause sympatric speciation?
genetic condition immediately causes reproductive isolation
when an organism has more than two sets of chromosomes
& cannot breed w/ parent pop
How punctuated equilibrium and gradualism describe two
different tempos of speciation.
Gradualism common ancestor and slow constant change
Punctuated- long periods of stasis punctuated by short bursts of significant change
Adaptive radiation
when many new species arise from a single common ancestor, , they fill different ecological niches/roles in their communities (that are extinct/dying) so they do not fight one another and the speciation rates raise, especially in places where a disaster occurs like in volcanoes
species in an isolated pop; change in gene frequency, a change in the environment, natural selection, and/or genetic drift.
will lose genes or alleles over time, which results in a decrease in fitness & local adaptation, and an increase in expression of deleterious or lethal alleles, they will diverge from one another, both in the way they look & genetically
Gradualism speciation
Common ancestor
Slow, constant change in morphology as they adapt
Punctuated Equilibium speciation
Eldridge & Gould
Long periods of stasis (no change)
punctuated by sudden change seen in fossil record
Hybrid Zones
Incomplete reproductive barriers
Possible outcomes: reinforcement, fusion(breakdown of reproductive barriers), stability
Morphology
by body shape, size, and
other structural features
Ecological
niche/role in community
How did life arise?
1) Small organic molecules were synthesized (amino
acids, nitrogenous bases)
2) Small molecules → macromolecules (proteins,
nucleic acids)
3) Molecules packaged into protocells (membrane-containing droplets)
4) Self-replicating molecules allow for inheritance
“RNA World”: 1st genetic material most likely RNA
First catalysts = ribozymes (RNA)
The age of the Earth and when prokaryotic & eukaryotic life emerged
Earth is 4.6 billion years old.
First life forms appeared 3.8 billion years ago
Characteristics of the early planet and its atmosphere
Early atmosphere = H2O
vapor, N2, CO2, H2, H2S
methane, ammonia
Energy = lightning & UV
radiation
Conditions favored synthesis
of organic compounds - a
“primitive soup”
Miller & Urey
Tested Oparin-Haldane
hypothesis
Simulated conditions in lab Produced amino acids
Methods used to date fossils and rocks and how fossil evidence
contributes to our understanding of changes in life on Earth
- Relative Dating:
- Radiometric Dating
-> can show an organisms adaptations to the Earth
Relative Dating
Uses order of rock strata to determine relative age of fossils
Radiometric Dating
Measures the decay of radioactive isotopes present in layers where fossils are found. (Half-life): # of years for 50% of original sample
to decay
Endosymbiont Theory Evidence
Mitochondria & plastids (chloroplasts) formed from small prokaryotes living in larger cells
1. Replication by binary fission
2. Single, circular DNA (no histones)
3. Ribosomes to make proteins
4. Enzymes similar to living prokaryotes
5. Two membranes
How continental drift can explain the current distribution of
species.
movement of continental plates changes geography & climate -> changes environ a species lives in which cause extinctions & speciation. + explain many similar species on different mainlands. (pangaea = supercontinent)
How extinction events open habitats that may result in adaptive radiation.
Extinction events open habitats bx when mass # species dies, another must fill its roll in the environment or its niche. The need to fill the ecological niche is what leads to adaptive radiation which is a period of rapid evolutionary change to fill an ecological niche.
Adaptive Radiation
Many new species arise from a single common ancestor
Occurs when: A few organisms make way to new, distant areas
(allopatric speciation)
Environmental change -> extinctions-> open up new niches for survivors
Evolution of new forms results from
from changes in DNA/ regulation of developmental genes
How behaviors are the result of natural selection
includes the ways that animals interact with other organisms & the physical environment and behavior is shaped by natural selection, behaviors increase an organism’s fitness + survival / reproduction
How innate behaviors increase survival and reproductive
fitness
provides the animal with the knowledge of when to do something that they need to do for survival (flower knowing when to bloom, birds knowing when to migrate), Ensures that activities essential to survival are performed correctly w/o practice
how does learned behavior increase fitness
the animal can learn a skill essential for survival/ climate change ex: habituation (loss of stimuli sense), imprinting
How organisms use communication to increase fitness
they use different types of communication ( pheremones, visual signals, tactile (touch), auditory signals) to reproduce, locate a food source, become aware of predators etc.
Role of altruism in kin selection
selfless behavior
Reduce individual fitness but increase fitness of others in pop (i.e. bee societies; naked mole rats) genes more likely passed down
Role of Inclusive fitness in kin selection
Total effect of producing own offspring (pass on
genes) + helping close relatives
kin selection: type of natural selection; altruistic behavior enhances reproductive success of relatives
