Evolution Flashcards
evolution 1
- All life forms are derived from previous life forms
- Genetic variation underlies evolutionary change
- Evolution yields anatomical and functional alterations over time
- changes in anatomy and function!
- Adaptation is specialization in response to particular environment
- Speciation is formation of distinct, reproductively isolated, life forms
Speciation
Speciation is formation of distinct, reproductively isolated, life forms
Reproductively isolated is how species are defined, life forms
Genetic variation
Random mutation produces genetic variation
Polymorphisms = sequence changes of different alleles
Gene pool = collection of all alleles for all genes in a population, ALL GENES IN POPULATION
Population = all individuals of a species in the same place at the same time, in same place at the same time*** not technically part of the same population of people who lived in NY 200 years ago**
Polymorphism
= sequence changes of different alleles, may have nothing to do with genes for different traits; even in parts of DNA can identify polymorphism in population some ppl have letters AAA in that spot, some have AAAT just part of variation you find in a population
Gene pool
Gene pool = collection of all alleles for all genes in a population, ALL GENES IN POPULATION
Definition of population
Population = all individuals of a species in the same place at the same time, in same place at the same time*** not technically part of the same population of people who lived in NY 200 years ago**
Genetic equilibrium
- means no evolution going on no change in allele frequency
- pretty rare and maybe impossible to be in genetic equilbirum forever, but true enough for periods of time that the model is worth using sometimes*
- so in order for a population to be in genetic equilbirum:
- Mating is random
- NO MUTATIONS, no net mutation
- Large population size
- NO migration in or out of population
- NO natural selection
Genetic equilibrium 2
Genetic equilibrium = no evolution = no change in allele frequency
Five conditions must be met for genetic equilibrium
Mating is random
Net rate of mutations is zero (i.e., A ← → a equal)
Large population size
No migration in or out of population
No natural selection
payoff for making these assumptions can use hardy weinberg assumptions/equations
Hardy-Weinberg equilbirum
key here p and q represent frequencies of alleles,
p dominant allele; q recessive allele will be decimals of less than 1
like .2 and .8= 1 which is 100% of alleles for that genetic locus in the population, we are assuming here in this version of Hardy Weinberg assuming only too alleles for this gene** we know out there there are some genes where there are more then 2 allleles, but Hardy-Weinberg assumes 2 for dominant and recessive
Hardy-W equ. 2
Hardy-Weinberg (HW) principle governs allele frequencies during genetic equilibrium
HW as applied to a two allele system (Bb):
p = allele frequency of dominant allele (B)
q = allele frequency of recessive allele (b)
p+ q= 1
Example: 75 BB, 125 Bb, 50 bb animals in population; p = 275/500, q = 225/500
Punnett square with allele frequencies dictates that square of equation is also true:
p2 + 2pq + q2 = 1 p2 = freq BB 2pq = freq Bb q2 = freq bb
Therefore, allele frequency is constant in each generation
Can calculate all frequencies from frequency of recessive phenotype (q2)
Hardy-Weinberg eq 3.
p2 + 2pq + q2 = 1
p2 = freq BB 2pq = freq Bb q2 = freq bb
Therefore, allele frequency is constant in each generation
Can calculate all frequencies from frequency of recessive phenotype (q2)
THE frequency of those genotypes and individuals in population, so first equation p+q=1 tells you abotu frequency of the alleles, this other equation tells you about hte frequency of different kinds of people or animals of genotypes you find in the population
for ex. this equation tells us if maybe individual homozgyous domiant, homo recessive, hetero of allele etc.. if you want to know frequency of homozygote individual is p2, homozgous recessive is the q2
if studying population homozgous recessive disease, if out of 100 ppl in population 1 person has the disease, telling you .01 is q2 which is by the easiest thign to measure in population; usually way in the easiest thing to tell, if see how many individuals in population have recessive phenotype and make it a decimal that is giving you q2, can also look at a populaton and see what portion of people have the domiannt genotype but not as helpful information do not know if homozgoute or heterozgyote, can be part of p2 group or 2pq cannot tell unless squence genomes, but if showing up with homogzgote recessive knwo genotype if know q2 can find q then find 2+p =1 then find p….
Frequency in HWE
if they say 20 individuals out of 100 have homoz. recessive genotype or homozgous recessive then 20 out of 100 would be genotype too, then the frequency would be 20/100 but make it a decimal so .2
same if population has 200 ppl, 40/200 would also be hte same as 20/100 also .2 in this case for the frequency in this case*
so may have to set up that fraction in order to get the frequency and then onc eyou have the frequency that decimal can use hardyweinberg equation
Evolution if violate any of the 5 things….
if violate any of 5 things mentioned population is evolvign! so if net rate of mutaiton is greater than zero, or population size is really small get what is calld genetic drift or migration in or out also called gene flow can change new people coming in means no combination of alleles coming in
Genetic equilibrium ≠ evolution
During evolution, allele frequencies are changing
If any one of five conditions is occurring in a population, evolution is occurring:
Net rate of mutation > 0
Natural selection
Mating is nonrandom (sexual selection)
Small population size (facilitates genetic drift)
Migration in and out of population (gene flow)
natural selection
Natural selection is the major driving force for evolution
Acts on PRE-EXISTING genetic variation in population
Selection increases frequency of helpful traits, decreases negative traits
Selects for individuals, not the group as a whole
Group selection (idea that evolution can sometimes select for group) is controversial
natural selection 2
watch out on mcat- say being treated with a certain antibiotic, the antiobiotic kills 99% of the bacteria causing your infection but 1% of that bacteria by random lucky chance has some mutaiton allows you to resist antibiotic being treated with so the presence of that antibiotic is then creating a selection pressure favoring bacteria that have resistance gene and can thrive even in the presence of that antibiotic so then the resistance bacteria will proliferate and become the dominant form of bacteria in your system overtime** MCAT will definitely test that concept but the way you would describe what is happening selection pressure in favor of resistant bacteria cells, or can say cells able to grow in the presence of antibitoic were favored, thrived able to pass down genes
what would be the wrong answer choice would be to say when antibiotic was intrdocued that CAUSSED some genes to mutate that caused mutations NOO just favors mutaitons that some lucky little cells happen to have because of sponatenous mutaiton*** doesn’t cause it it favors***
Fitness
The more an organism or individual passes on its genes the more fit it is! so the way this has been tested on the MCAT which of the following individuals i teh most fit, 18 year old track star or 85 grandma with arthritiss, in this context the grandmother is more fit than the kid because she has passed on her gene more***
test difference btw evolutionary fitness and atheltic fitness under other circumstances*
Fitness 2
Reproduction generally yields more offspring than can be supported by environment
Fitness reflects ability of an individual to survive and reproduce
Two components of fitness: mortality and fecundity
Mortality = death
Fecundity = # of offspring
Fitness is specific to a particular environment
Drought resistant plants are more fit in desert, but not in rainforest
If organism has higher fitness than peers, frequency of its alleles will increase
Fecundity
Fecundity = # of offspring
Inclusive fitness
A gene maximizes its chance of survival by promoting the survival and reproduction of similar and closely- related individuals
Related to the concept of kin selection
Used to reconcile cooperation between organisms with the idea that genes “selfishly” promote their own survival
Example: animals sacrificing themselves so that a group of relatives survive. Ultimately, this will cause more copies of their genes to exist
Inclusive fitness 2
From darwin’s point of view, want to pass on our genes! But it is allso true when our siblings or cousins have kids we want this, the idea of inclusive fitness takes that into account sometimes we will make sacrifices for other members of our family from darwin point of view can explain that by saying when our relatives reproduce genes that we share with them are getting passed down so can make sense of it even from within this very genetically focused perspective
Nonrandom mating
In environment, mating is generally nonrandom = sexual selection
Some phenotypes are preferred mates
Individuals may prefer phenotype similar to their own → positive assortative mating
Individuals may prefer phenotype dissimilar to their own → negative assortative mating (opposites attract)
Preferred mates have higher fecundity (average # offspring) more genetically productive kind of mating*
genetic drifit
change in allele frequencies that are not just random, when populations are small tend to be changes in allele frequency because of genetic drift
2 examples: bottleneck effect and founder effect
bottleneck
natural disaster dramatically dec size of population
alleles that reamin after diseaser are over represented by chance, another allele can be removed from population becuase rare to begin with and everyone who had it died, so can change allele frequency by cutting down population randomly*
Founder effect
similar idea, takes smaller population group; story of migration group some small part of the population moved to a new place and founded a new population maybe came to the new world from europe or subgroup of population went somehwere else, in new population they found different than they were in original population that the colonists came from
key is it is a different population, bottleneck effect everyone stays in oen place lots of ppl die; founders effect think about europeans coming to new world, point is both of those scenarios create changes in allele frequency** and that is evolution, evolutionary change
Genetic drift, bottleneck effect, founder’s effect
In small populations, allele frequencies more likely to change stochastically (randomly)
Example: allele frequency is 10% in two populations (1000 organisms vs 10)
So, 100 alleles in first population, but just 1 allele in second
By chance, allele much more likely to be eliminated from second population
As a result, small populations undergo genetic drift
Bottleneck is an example of genetic drift
Bottleneck is a rapid decrease in population size, eliminates most alleles
Bottleneck reflects adverse selective pressure (famine, disease, etc)
Remaining survivors carry just a few alleles
When population re-expands, low genetic diversity is dominated by “founder” alleles
Classic example two ponds separate but close to eachother….
heavy rain ponds become two ponds, that would be suddenly all alleles are able to mix together
GENE FLOW
Gene flow
Separate populations have different gene pools
Mixing of populations transfers alleles
Genetic diversity increases within population, decreases between populations
Example: flooding links two previously separate frog ponds
Bottleneck effect vs. founders effect 2
Bottleneck is an example of genetic drift
Bottleneck is a rapid decrease in population size, eliminates most alleles
Bottleneck reflects adverse selective pressure (famine, disease, etc)
Remaining survivors carry just a few alleles
When population re-expands, low genetic diversity is dominated by “founder” alleles
species and speciation
Species is a population that can interbreed with itself but not other species
All members can interbreed and produce viable fertile offspring
One species placed in different environments → evolution and speciation
Two groups different species if environmentally isolated, cannot mate with eachother and produce fertile offspring; or can be in same place but not be able to reproduce with eachother***
speciation defined as: the formation of new and distinct species in the course of evolution.
REPRODUCTIVE ISOLATION OF SPECIES
categorized into prezygotic before fertilization maybe reproduce in differnt places, different courtship rituals, or gametes do not stick together properly
maybe they do reproduce but progeny are steril or progeny die, so for whatever reason in process reproduction doesnt work properly ex mule sterile
Reproduction isolation of species 2
Several barriers to interbreeding of species
Barrier can be prezygotic = before fertilization
Reproduction in different times and places (e.g., seasons)
Different courtship rituals
Mechanical incompatibilities in copulation
Gametes may be incompatible (e.g., sperm cannot bind and get into egg)
Barrier can be postzygotic = after fertilization
Progeny may be sterile (e.g., female horse × male donkey = sterile mule)
Progeny may not complete development
Progeny in second or later generations may be inviable
Gene leakage = gene flow between species
prezygotic
and
postzygotic
Barrier can be prezygotic = before fertilization
Barrier can be postzygotic = after fertilization
Ecological Niche and Competition
Where an organism or population lives and reproduces
Defined by conditions necessary for growth and survival (food, temperature, light, etc)
Ecological niche includes competitive interactions among populations
Populations indirectly compete for limiting resources or directly interact (e.g., predation)
No two populations can occupy the same niche!
One population will move out, die off, or evolve to occupy another niche
Symbiotic relationships between species (mutualism, commensalism, parasitism)- living very closely with eachother, three kinds
mutualism= ++
commensalism= +/0 one benefits other one doesn’t care
parasitism= +/- situation one species benefits other is harmed by interaction
Just b/c cannot have two populations being in the same place in the same way
Optimal foraging theory
Idea from ecology that animals forage in such a way as to maximize their energy uptake per unit time- basically organsims are smart about foraging if can stay where they are eat little berries, low cal but plentiful and do not have to go anywhere will do that and not expend a lot of energy, if can get enough calories where they are they would only make a difficult journey if they needed to so if the bear runs a few 100 miles get better food or more nutrient rich food, but this theory says that organisms is aware of tradeoff will not run 200 miles for nothing if organism expending a lot of energy to get food has to be high calorie and worth it
Organisms adapt strategies that encourage them to intake the most calories while exerting the least effort
Different foraging strategies have evolved depending on both an organism’s environment and how much that environment has changed
An unstable environment will lead to a more flexible diet
Evolutionary game theory
The application of game theory to understanding the strategies that organisms in a population use in competition
Unlike in classical game theory, the goal is not the “best” strategy, but a strategy that is stable against others in a population
Often used to explain phenomena between species such as co-evolution and cooperation
Basically game theory scenarios ppl cooperate with eachother, choices individuals make in differnt scenarios if everyone cooperates everyone gets biggest reward if evyerone chooses to cooperate and you don’t then you are screwed so it show you decide to relate to other players, cooperation vs competition in context of game theory some ppl tryign to apply this to evolution and talk about choice btw competion and cooperation
types of selection
Most phenotypic traits are polygenic = controlled by many genes
Most traits have a bell-curve distribution around a mean (e.g., height)
Three different kinds of selection
- Stabilizing selection
- Directional selection
- Destabilizing selection
stabilizing selection
eliminates extreme phenotypes, narrows curve around mean
if environment really stable, whatever color most common see more and more mice with phenotype that is facored like in this case medium fur*
directional selection
- favors one extreme over the other, shifts mean value
- now what happens is htere has been some kind of enviornmental change, maybe there are examples from industrial revolution buildings dirty animals darker coloration could hide better so did better, something changing what phentoype is most favored in this environemnt
- so maybe going further dark phenotype more favored, most favored phenotype is shifting one direction or another!
destablizing selection
- eliminates intermediate phenotype, splits distribution in two
- Destabilizing selection may promote speciation
- environemnt becomes pathcy, if light fur can go to one place, dark fur can go ot another place, but if medium fur stuck
- so here get two distinct phenotypes within population favored, destablizing selection can in some cases lead to sepciation
- if light colored mice hang out in one environment adn dark colored mice hang out in another area and stop interacting with eachohter can no longer breed with eachother that point down teh line refer to them as different, they will no longer interact with eacother
remember speciation is defined as: Speciation is how a new kind of plant or animal species is created. Speciation occurs when a group within a species separates from other members of its species and develops its own unique characteristics.
the formation of new and distinct species in the course of evolution.
r-selection
Evolution yields two evolutionary strategies for species
When environment is far from its carrying capacity, less competition for resources. Some organsims are r-selectd some are k-selected species
Evolution will favor “r-selected” organisms
r-selected species have: many offspring, rapid development, little parental care, small body size, short lifespan, high mortality (e.g., insects, amphibians) THINK INSECTS, have lots of offspring develop rapdily with very little interaction help from parents, strategy is to put lots and lots of offspring out in world and let them go
When environment is near or at carrying capacity, more competition for resources
k-selection
Evolution will favor “K-selected” organisms
K-selected species have: few offspring, long gestation, more parental care, larger body size, longer lifespan, lower mortality (e.g., humans, primates)
Very few offspsring, large gestational period, don’t die as much can see how the lists go together, how having many offpsring without much invcestment in them versus few offspring with high investment is another strategy
With few offspring makes sense those offspring would be larger, live longer better cared for, see organisms that adopt one or the other of these approaches
Divergent evolution
Divergent evolution is evolution of two species away from a common ancestor
Divergent evolution = adaptive radiation
Homologous anatomical structures have a common evolutionary origin
Example: dog foreleg, human arm, whale front flipper
Implies common ancestor or common ancestor structure, can identify homolgous structures that A and B have, big example of this some ancestoral structure gives rise to forearm of human, front flipper of whale, wing of a bat, all of those are derived from a common ancestoral structure adnd they are called homoglous structures** they have a common ancestor* but the structures have different functions in present like whale front flipper for swimming, dog foreleg for running, bat for flyign but homolgous come from common acnestoral structure
convergent evolution
Convergent or parallel evolution
Unrelated organisms may evolve similar anatomical structures
Structures can arise in parallel = more than once, in different evolutionary lines
Similar structures that evolve from different ancestors = analogous
Example: bird wing, insect wing
NO homolgous strucrures because no common ancestor, but get insect wing and bat wing not both derived from acnestoral wing, just that being able to fly which is a HUGE advntage from evolutionary poitn of veiw so tehy are analgous same function in present but do not imply an evolutionary relationship
adaptive raditation
common acnestor derived homologous structures for divergent evolution
ex. darwin finches all started on mainland, adapted to other islands once flew out differnt beaks became differnt from eachother that is another example of adaptive radiation all started on mainland and then the finches moved out to island all adapted*
Molecular evolution and relatedness
know all life forms use the same genetic code! and there are some genes that are highly conserved, i fyou want to make inferences about how closely realted differnt organisms are or different species are the best thing to do is look at how much dna they have in common, how much sequence is in common
Molecular evolution and relatedness 2
Evidence for evolution is present in fossils and DNA
Fossils provide evidence of anatomical relatedness and alterations over time
DNA sequence data indicates genetic similarity of species
All life forms share universal genetic code
Genetic code evolved once, was conserved (maintained) in all life forms
Sequence and function of many genes is also conserved across species
Key genes are highly conserved and do not change much over evolution
Evolutionary distance is indicated by degree of sequence homology
More evolutionarily distant = more sequence changes
Assumes mutation rate is generally constant
“Horizontal” swap of DNA among species can complicate evolutionary trees
Ontogeny
Ontogeny = embryonic development
when embryo developing goes through all evolutionary stages, not always true when human embryo is developing not fast fowarding through all of human evolution going through phase reflecting lower animals, but it is true human has tail for a while so there are other less advanced evolutionary forms that embryos do go through, cornel of truth to this not strictly true but lot can see about evolution when look at embryos
Homologous structures look really similar when preparing embyos
ontogeny and phylogeny
Ontogeny = embryonic development
Phylogeny = evolutionary development of a species
During development, embryo passes through developmental stages
Developmental stages resemble evolutionary predecessors
Anatomical structures shared by related species tend to develop earlier
Example: backbone in fish and mouse
Homologous structures look similar in embryo
Anatomical structure specific to one species tend to develop later
Example: human cerebrum
Anatomical structures that are lost during evolution are lost later during development
Example: leg bones in snakes and whales
Anatomical evolution generally occurs by modifications of developmental plan
Changes in DNA affect morphology of embryo and its development
Vestigial structures
Structures that serve no purpose!
Vestigial structures/organs serve no obvious or useful function = evolutionary relic
Related to useful structures in other species
Indicative of common ancestry, followed by evolutionary specialization
Human coccyx, appendix, snake limb bones, eyes of blind cave-dwelling fish
Like snakes have limb bones but obviously do nto need those and dont’ walk but can see verstiage of evolutionary history, some fish live in really dark vaces still have eyes because evolved from fish that dif have vision*
Chordates
we are in phylum chordata, we are chordates which includes all vertebreates
Chordates have four basic features:
Notochord* remember only for a little while as embryos, mesodermal structure gives rise to neural tube that gives rise to brain and spinal cord, some features common to all chordates are only present in embryo; part of being a chordate*
Dorsal nerve cord (dorsal to notochord) dorsal= back
Pharyngeal pouches/gill grooves (in land animals, lost during embryogenesis) somethign have briefly in embryos which we do not have after
Post-anal tail: extension of notochord, lost in humans and frogs; humans lost tail, purely found in embryos, stil qualifies us as chordates
Within phylum of chordates all vertebrates are included
In contrast, arthropods (insects, crustaceans), annelids (worms) have ventral nerve cord
Vertebrates classes
Animals are either invertebrates or vertebrates
Invertebrates lack a backbone (e.g., sponge, fruit fly)
Vertebrates have a backbone (e.g., humans, mice, crocodile)
Main classes are fish, amphibians, reptiles, birds, and mammals
Warm blooded organisms can actively regulate body temperature = birds, mammals, if we go somewhere really cold do not just equilibirate with environment we are able to regulate
Cold blooded organisms cannot regulate body temperature = fish, reptiles, amphibians
Temperature of cold-blooded organisms dictated/controlled by surroundings
On a hot day, lizard sits in shade to cool off
Relations of vertebrate classes
Fish were the first vertebrates
Fish have 2-chambered heart (one atrium, one ventricle)
Amphibians evolved from fish, are able to breathe air w/ lungs, but still inhabit water
Amphibians have 3-chambered heart (two atrium, one ventricle)
Reptiles evolved from amphibians, live mainly on dry land
Reptiles have 3-chambered heart (two atrium, one partially divided ventricle)
Birds thought to have evolved from reptiles
Birds have 4-chambered heart, are warm-blooded
Mammals thought to have evolved from reptiles
Mammals are warm-blooded, have 4-chambered heart, mammary glands for nursing
Origin of life
idea very early atmosphere had no molecular oxygen, water present so oxygen in water; ammonia present, so idea is that the high energy lightenign storm UV light bombarding early atmosphere jolted all these inorganic moelcules ttogether to form orgnaic moelcules amino acids and nucleotides of RNA
All current life forms are genetically similar
Life probably evolved only once, from simple chemical molecules
Early earth: no oxygen, but simple organic molecules and energy
Miller experiment: inorganic molecules + energy → organic molecules, took ammonia and water zapped them like crzy and showed yes randoly can get organic molecules and amino acids from doing that
So the idea is that the first “organisms” ppl with reproduction would have been squiggles of rna becuase can act as catalyst for interactions, code information, squiggle with RNA genome, can reproduce itself, self replicaitng RNA may have been earliest life form some ppl refer to RNA world as world of rna squiggles
Water, ammonia, methane, hydrogen + spark → amino acids, nucleotides
Origin of Life 2
After chemical evolution, possibly and RNA world
RNA can be a catalyst, RNA can encode information
Self-replicating RNA may have been earliest “life form”
After RNA world → eventually organisms
Eventually dna developed from RNA, and cells evolved from that point on life was DNA based
Last common ancestor is theoretical ancestor to all present life forms
First cells were anaerobes, then photosynthetic autotrophs → oxygen
Once photosynthetic autotrophs evolved suddenly oxygen in atmosphere, once there was oxygen heterogrphs many animals were able to develop from there
know the order this happens:
inorganic molecules– organic molecules–> RNA–> DNA–> photosyunthetic autotrophs–> heterotrophs
the inorganic source of carbon peope thing of is methane**** organic molecules can think of as amino acids
Taxonomy
King KINGDOM- broadest
Phillip PHYLUM
Came CLASS
Over ORDER
From FAMILY
German GENUS e.g. Homo
Soil SPECIES e.g. sapiens
So when we say homo sapiens, homo is our genus sapeins is our species
how they test- if two organisms are in the same genus, they must also be in the same family, order*** SAME EVERYTHING ABOVE BUT NOT BELOW*** so not same species
same class, same phylum, but not same order family genus species
Types of selection graphs
Converging versus diverging evolution graph
