Unit 7: Evolution Flashcards
Evolution
the process of a population of organisms changing over time to be better adapted to their environment
- happens through the genetic information within the species
individuals CANNOT evolve, only POPULATIONS can evolve or MULTIPLE generations
- don’t mutate to evolve, mutations occur naturally and environment dictates which mutation is most beneficial
Natural selection
the process that drives evolution
“natural” b/c it happens in nature, “selection” because these forces select for which organisms are best adapted to their environment
*not selection with intention, natural doesn’t have a brain so it can’t actively pick a better or worse trait
Natural variation
every population has variation in every aspect (naturally occurs through unintentional mutations and intentional meiosis) - slight differences
only clones are exempt from natural variation
any slightly beneficial variation= Adaptation and must be INHERITABLE to play a role in natural selection
Four fundamentals of evolution
V - variation
I- inheritance
D- differential survival (Fitness)
A- adaptation
Artificial selection
driven by humans - we select which traits are better for US but not the population. We create new species that serve specific functions for us
Directional selection
creates pop where most individuals have extreme trait, and the other extreme is very rare
- graph shifts horizontally towards one end or the other
ex. giraffes, good to have long neck and longer necks survived longer bc of access to food, so giraffes evolved to have really really long necks (og giraffes looked like horses)
Stabilizing selection
creates pop where majority of individuals have average trait (both extremes are rare/also can be bad)
- graph narrows towards middle
ex. human babies, small babies died and big babies got stuck and died and killed mom too so the middle is the good spot for babies’ weights
Disruptive selection
creates pop where most individuals have one of two extremes (avg is bad)
- graph has two humps at each extreme and a dip in the middle
ex. peppered moths, black and white blend in well in their respective environments, grey doesn’t blend in with anything
Forces of evolution
Natural selection: variations that are more advantageous survive and pass on genes change gene frequencies
- ALWAYS adaptive
Mutations: random DNA changes = change in gene pool + gene frequencies
- Not always adaptive
Migration: organisms move between populations (gene flow) and when organism migrates, they take their genes with them and alter the gene pools in the population they left and the pop that they joined
- not adaptive (organisms can move to environments they aren’t adapted too)
Genetic Drift: random changes in the gene frequency (RANDOM CHANCE)
- most impactful on a small population b/c each individual matters more
* Bottleneck effect: really big pop drastically reduced to small pop suddenly
* Founder effect: large pop and small group from pop leaves to start new pop somewhere else they haven’t previously existed, smaller gene pool is hit harder by genetic drift
Non- random Mating: when organisms choose who they mate with, so genes aren’t randomly mixed in each generation = gene frequencies are changing
- sometimes example of sexual selection
Microevolution vs Macroevolution
Microevolution: changes to the DNA of a population (genetic level) - this needs to happen before there are physical changes/ macroevolution
- Gene pool: collection of all the alleles for a trait (# of individuals x 2)
- Allele frequency: # of dominant or recessive over total alleles in gene pool
- Genotype frequencies: # of individuals with genotype over total pop
Macroevolution: physical changes to population, how their phenotypes have changed and evolved must have microevolution happen before this can happen
Harvey Weinburg Equations
p = frequency of dominant allele
q= frequency of recessive allele
p + q = 1
p^2 = frequency of homozygous dominant
2pq = frequency of heterozygous
q^2 = frequency of homozygous recessive
p^2 + 2pq + q^2 = 1
Always find the q value and then you can find everything else
Harvey Weinburg Equilibrium
when a population isn’t evolving and gene frequencies aren’t changing
To be in this state, population must have:
1. no natural selection
2. no mutations
3. no migration
4. no genetic drift
5. perfectly random mating
IMPOSSIBLE so this equilibrium DOESN’T EXSIST
- becomes a theoretical comparison point for real world populations
Species
a group of organisms that can successfully interbred and create VIABLE, FETILE, offspring
Speciation
the formation of a new species increasing biodiversity + strengthening ecosystem
- RPRODUCTIVE ISOLATION = always the end result of speciation (two pops so genetically different they can no longer interbreed)
Allopatric or sympatric are the two types
Allopatric Speciation
speciation that takes place in completely separate environments
GEOGRAPHIC ISOLATION (only type of allopatric speciation): a real physical barrier that separates a population into two groups and can no longer reach each other so they become two species
* not all barriers are barriers for all species
Sympatric speciation
speciation that takes place in overlapping/nearby environments and ecosystems
- Sexual selection, prezygotic barriers, and postzygotic barriers
Sexual Selection
Type of sympatric speciation: when different sub population starts selecting for different traits in partners rapidly causing, the 2 populations to separate (ex. female birds attracted to different traits and mate with those)
Pre-Zygotic Barriers
barriers that prevent sperm and egg from ever meeting
- HABITAT ISOLATION: different habitats so populations don’t meet (birds living on different layers of trees)
- TEMPORAL ISOLATION: mate during different times of the year so they can’t mate together
-BEHAVIORAL ISOLATION: different behaviors attract different species (their courtship behaviors) so works the same as sexual selection instead of physical traits it’s behaviors
- MECHANICAL ISOLATION: incompatibility in body structures (physically can’t mate)
Post- zygotic barriers
barriers that lead to offspring that are less successful/productive, and evolution discourages their existence
- REDUCED HYBRID VIABILITY: offspring is born, and less healthy/successful b/c parents’ sources of genes don’t work well together (almost never make it to adulthood
- REDUCED HYBRID FERTIITY: hybrid can’t reproduce (ex. mules and ligers)
Adaptive radiation
organism colonies a new area and gains access to new ecological niches or an extinction event opens new ecological niches
- one ancestor species gives rise to multiple new species in relatively short evolutionary timespan
ex. Darwin finches, all from same species
Punctuation Equilibrium vs Gradualism
PUNCTUATIED EQUILIBRIUM: short moments of fast evolution followed by long periods of time with little to no change (“fast evolution”)
GRADUALISM: accumulate slow incremental changes over time, slow + consistent (“slow evolution’)
Extinction
Population has three options when things get hard:
1. adapt + evolve
2. migrate
3. die (doesn’t adapt fast enough or can’t migrate)
Extinction is natural, normal, and always happening
Mass extinction is also normal but rarer (this is when the rate at which species go extinct is much higher than normal)
- mass extinction allows for adaptive radiation and leads to an increase in species diversity
-there have been 5 mass extinctions and probably entering 6th caused by humans
geographic data
location data (organisms with similar traits found in similar areas
ex. birds of paradise and ungulates
fossil data
learning by using fossils (tells us where, what it ate, etc)
- trace fossil (mold/impression or coprolite (poop))
- body fossils (remains. bones and super super rare)
Geologic data
the law of superposition (young on top, old is deeper) helps determine the RELATIVE AGE OF FOSSILS
- this comparison isn’t very specific which is why there is RADIOMETRIC DATING
radiometric dating can determine exact age of rocks/fossils (within a few thousand - million years) by finding out the amount of radioactivity in the rock
*The traits, location, and age of fossils tell us about a species
Morphology
study of body shapes and body structures (see how close or distantly related organism are)
-homologous structures
- analogous structures
-vestigial structures
- comparative embryology
*Great for seeing physical similarities and differences but analogues structures can trick you so sometimes morphology doesn’t tell you how closely/distantly related organisms are
homologous structures
similar STRUCTURES b/c of common ancestors but they don’t have the same FUNCTIONS b/c of different environment + adaptations
ex. humans and cat have same bones but humans don’ walk on their hands
this is DIVERGENT EVOLUTION: 2 (or more organisms are descended from same ancestor but evolved along different pathways
analogous structures
similar FUNCTION but different STRUCTURE b/c no common ancestor/distantly related but similar environmental pressures
ex. wings, birds and bugs evolved to fly but they aren’t closely related
this is CONVERGENT EVOLUTION: 2 organisms have different common ancestors but have same structures and traits b/c of similar evolutionary pressures
vestigial structures
organisms have reduced size +function (traits are useless) but they show relationships to organism where those structures are still used (show what ancestors/past organisms used to do)
- these useless traits will sometimes be there and sometimes not b/c evolution only gets rid of bad things (if vestigial structure is neutral, it will remain a part of the organism)
ex. whales have femurs and hip bones showing that their ancestors used to walk, and they evolved to only swim
Comparative Embryology
embryos of developing organisms show us how organisms develop (similar embryos = similar/common ancestors)
Molecular DNA
we can analyze molecular makeup of organisms with modern tech (only available for past couple decades)
- DNA sequence is ALWAYS most reliable and accurate data source (tells you exactly how related organisms are)
- Amino Acids are the SECOND-BEST way to see how similar organisms are (the redundancy of codon codes means this is less reliable, specific, and accurate)
Phylogenetic tree
tool used to visually show evolutionary relationships b/t organisms
Shows:
1. relationships (close vs distant) ALWAYS
2. time between organisms (optional)
3. characteristics that distinguish organisms (optional)
Outgroup
the least related group on a phylogenetic tree
Ancestral vs Derived traits
ANCESTORAL: older trait often shared by many descendants across many species
DERIVED: more recently evolved, seen in fewer species
*When trait is shown on phylogenetic tree, ANY organism after the trait has the trait
Ancestral and derived are like a spectrum it’s not one of the other (one trait is more derived than another, it’s all relative to how detailed the tree is as well)
Node
most recent common ancestor between 2 species (any place where the branch is/ where the tree splits)
organisms that share a more recent node are more closely related
- Any node can be flipped 180 degrees, the trees are about the order of the nodes rather than positioning
