Download How do we know evolution is a thing? 1) ​Fossil record:​variations

How do we know evolution is a thing?
1) ​Fossil record:​ variations in species over time due to changes in environment and behavior give rise to new
species
2) ​Biogeography:​ similar but unrelated species can be found all over the world as a result of environmental
influences
- Fun fact: emus, kiwis, ostriches, and rheas are all unrelated, flightless birds from Australia, New
Zealand, Africa, and South America, respectively
3) ​Molecular biology:​ the higher the % of shared genetic information between two species, the closer their
evolutionary relationship
4) ​Comparative anatomy:​ remember homologous and analogous structures? They’re back:
- Homologous structures:​ (top image)
- “homo” means “same,” so organisms with homologous structures have the ​same​ common
ancestor
- Humans and cats are different species, but we share homologous structures as pictured
- Both the skeletal structure ​and​ alignment are similar, but their purposes may be different
- Analogous structures:​ (second image)
- think “analogy;” these structures are similar like a domino effect is similar to a chemical
reaction (but they’re not the same)
- Analogous structures are a result of ​similar environments​, ​not​ a
common ancestor
- The insects do not have a similar skeletal structure, but their wings
serve the same purpose as the birds’
5) ​Embryology​: notice how similar different species start off looking as embryos.
- The similarities and differences between different species can help scientists
determine how closely related different species are evolutionarily.
- Phylogenesis:​ the evolutionary background of organisms like
those below (their similarities and differences)
Natural Selection
- Natural selection is how organisms with specific traits/adaptations are selected for or against in an environment (those that have the more useful traits are
able to reproduce and pass on said traits = ​survival of the fittest​)
- occurs because ​competition​, ​genetic variation​, and ​limiting factors​ keep populations ​fit​ and ​stable​ even though they may have a huge ​reproductive
potential​ (families could have dozens of kids, but they don’t)
Stabilizing selection
Favors more ​common​ traits
- kind of like a compromise, these conditions favor Goldilocks
conditions (not too hot, not too cold, ​just​ ​right​) while selecting
against extremes (bye-bye Mama and Papa Bear)
Directional selection
Favors ​one​ extreme while selecting against the other
- In an environment w/more bushes and trees: long-necked
tortoises​ > short-necked tortoises, bc the long-necked ones can
get food more easily and are more likely to reproduce and pass
on their adaptations.
- Have you heard of ​MRSA​? This antibiotic-resistant strain of
bacteria is a result of directional selection favoring
antibiotic-resistant bacteria (since all of the non-resistant strains
are dead)
Disruptive selection
favor ​both​ extremes while selecting against common traits
- in rocky, gray mountains, gray and black bunnies would
camouflage better than the more traditional/common white
bunnies, resulting in disruptive selection (population would shift
from being mostly white to mostly gray ​or​ black)
Sexual selection
selective mating where females (or males) select male mates
based on physical traits/behaviors that they deem more desirable
- This is because females generally put in more energy
(incubating eggs, feeding babies, etc)
- ​How?​ fancy plumage, dances, manes, songs, hormones,
competitions attract mates
- This can lead to ​sexual dimorphism​ -- stark differences in
appearance btwn male and female (Cardinals)
Artificial selection
humans manipulate populations/species to produce specific traits
- Breeding for a specific type of pet: calico cat, fluffy dogs,
friendlier puppies
- Breeding for a desired attribute: juicier, larger fruits or
cabbages
Where do these variations in the gene pool come from?
1) ​Mutations!​ This is the only kind of event that introduces never-before-seen alleles into the gene pool
2) ​Sex:​ meiosis has three main sources of genetic variation: crossing over, independent assortment, and random fertilization
3) ​Diploidy:​ in 2n/diploid organisms, heterozygotes have two copies of a chromosome and can store ​two​ different alleles while only expressing one (ie:
you could be heterozygous for eye color and store the allele for both blue and brown eyes but only express brown eyes)
4) ​Outbreeding:​ random mating (not encouraged among humans = STDs) but is otherwise beneficial since it introduces alleles from different populations
5) ​Balanced polymorphism:​ appearance of 1+ phenotypes in a population: in most populations, one allele is the most advantageous but the other less
advantageous alleles may still exist because they are helpful for other reasons.
a) Heterozygote advantage:​ In parts of Africa, an abnormally large percentage of populations suffer from sickle-cell anemia (hemoglobin, the
oxygen-carrying protein, is malformed and is less efficient at transporting oxygen throughout the body). However, this seemingly unfavorable
disease makes victims immune to malaria (but can still kill them).
Heterozygotes have an advantage (since sickle-cell anemia is a recessive disease) since they have a combination of both normal and abnormal red
blood cells ​and​ are immune to malaria:
b) ​Hybrid vigor/Heterosis:​ ​inbred​ heterozygous offspring are often of superior caliber/quality than their parents because the unfavorable (most
likely recessive) alleles are overshadowed by favorable (most likely dominant) alleles, resulting in an overall ​better​ specimen
c) ​Frequency-dependent selection/minority advantage:​ rarer phenotypes have the most obvious advantage in predator-prey relationships. Predators
may have a specific picture of their prey, so if a prey looks different from the more common picture, it has a higher chance of surviving and
reproducing. But, this novelty eventually fades when the “minority” eventually becomes the “majority” and the predators realize.
Hardy-Weinberg Equilibrium:
Conditions that must be met for a Hardy-Weinberg situation:
1) BIG population
2) Isolated population
3) Random mating
4) Neutral selection/no natural selection
5) No mutations
Why? Because a Hardy-Weinberg population is a population that is not evolving and is considered to be at ​genetic equilibrium​. Only then do allele frequencies
stay constant. They can be calculated with the equations: 1) p + q = 1 2) p2 + 2pq + q 2 = 1
-
Equation 1 only takes alleles into account while equation 2 takes the population and alleles into account.
You can assign the p or q to the dominant/recessive trait
What causes populations to experience evolution and changes in their gene pools?
1) ​Natural selection​ favors certain characteristics and causes allele frequencies to shift towards an extreme/extremes/common ground
2) ​Mutations​ produce new alleles altogether (good ​or​ bad)
3) ​Genetic drift​ is just when Mother Nature trolls gene pools and ​randomly​ causes changes in allele frequencies
a) Bottleneck effect:​ a sudden reduction in the population due to who-knows-what can drastically diminish the amount of genetic variation/certain
allele frequencies within a population and make them more sensitive to changes in the gene pool
b) Founder effect:​ if a small part of a population branches off and isolates itself, founding a new population, this can lead to an increase/decrease in
allele frequencies that were not as apparent in the larger, original population (Amish ppl might have 6 fingers/toes instead of 5 bc they cut
themselves off from modern luxuries via isolation)
4) ​Nonrandom mating​ can lead to changes in allele frequencies if the males/females prefer particular behaviors/characteristics (I don’t really know why,
but many girls (I am a girl) prefer tall guys (I don’t really care… back to biology!)
Where did that panda come from
SPECIATION -- ​the development of new species. Here are the different mechanisms:
Allopatric speciation
- think “another Fatherland” = another place = geographic
isolation
- ​G​ilbert R
​ ​ealizes ​Di​ fferent ​R​ebellious​ ​S​pecies
Geographic isolation → reproductively isolated population →
differential evolution → reproductive barriers develop btwn
diff populations → new species!
- If two populations of a species are separated over a period of
time, they will eventually adapt to their different environments.
This could lead to changes in reproductive anatomy/behaviors
that no longer allows them to mate = new species
Sympatric speciation
- think “same land” = both stuck in the same place = new
species forms w/o regard to geography.
1) ​Balanced polymorphism:​ since polymorphism is the
presence of multiple phenotypes, this means that only
organisms with the same phenotype can mate with each other
(even though they might start from the same species).
Eventually, they may become different enough to become a
different species.
IE: on right, guppies that are larger and brighter have evolved
to be different from the smaller, duller guppies due to different
predators.
2) ​Polyploidy:​ having more than sets of chromosomes
(tetraploidy = 4, etc) due to nondisjunction. All in all, more
chromosomes = more alleles = immediate speciation since the
offspring is reproductively isolated from the start (have fun
finding a mate)
3) ​Hybridization:​ two species → hybrid baby. Hybrid baby may
eventually evolve differently enough to become a new species
(if the environment is different enough)
Balanced polymorphism:
http://www.sbs.utexas.edu/levin/bio213/pop
gen/guppyselection.3.gif
Polyploidy & Nondisjunction:
Adaptive radiation
One common ancestor → rapid speciation/divergence into
many different species due to a diverse environment
IE: Galapagos islands: one finch → hundreds of species of
finches w/different beaks, wings
But what if they randomly get back together… couldn’t something happen then?
Nope. Once speciated, always speciated (basically):
How to maintain PREZYGOTIC reproductive isolation:​ - these are all predetermined/before fusion of gametes has occurred
1) Temporal isolation: different sex times (frogs and birds mate seasonally)
2) Habitat isolation: if you don’t see your potential mate, you will not mate
3) Behavioral isolation: that tail-wag might mean “yes” to some, but “NO” to others
4) Mechanical isolation: reproductive organs do not fit
5) Gametic isolation: the male and/or female gametes do not recognize each other
How to maintain POSTZYGOTIC reproductive isolation:​ - these are all measures ​after​ the gametes have fused/zygote has formed
1) Hybrid inviability: zygote cannot develop so it dies
2) Hybrid sterility: hybrid cannot reproduce (mules)
3) Hybrid breakdown: hybrids’ offspring are fragile and die
Bibliography:
1) Homologous structures: ​http://2.bp.blogspot.com/-DbM3P9U0AdE/Vp7XwklrxSI/AAAAAAAAAOM/YGaB9frFFuk/s1600/cats.png
2) Analogous structures: ​https://s-media-cache-ak0.pinimg.com/564x/fc/04/20/fc0420e34b7ea49bf5cbf72b51ac295e.jpg
3) Embryology:
http://lh4.ggpht.com/_yItZwKwfM-I/TVeixSGzqXI/AAAAAAAABIU/lCN6Jqh9-fk/embryological-evidence%5B23%5D.jpg?imgmax=800
4) Goldilocks: ​http://www.santagames.net/images/stories/goldilocks/goldilocks-3.jpg
5) Stabilizing selection: ​https://www.pathwayz.org/Node/Image/url/aHR0cHM6Ly9pLmltZ3VyLmNvbS9CNVpTZ3NQLmpwZz8x
6) Directional selection: ​https://i0.wp.com/avonapbio.pbworks.com/f/directional_selection.gif
7) Disruptive selection: ​http://bio.research.ucsc.edu/~barrylab/classes/animal_behavior/IMAGES2.DIR/DISRUPT.GIF
8) Artificial selection: ​http://evolution.berkeley.edu/evolibrary/images/evo/mustardselection.jpg
9) Cabbage: ​http://evolution.berkeley.edu/evolibrary/images/evo/mustardselection.jpg
10) Heterozygote advantage: ​http://blog.canacad.ac.jp/bio/BiologyIBSL2/files/1858017.GIF
11) Guppies: ​http://www.sbs.utexas.edu/levin/bio213/popgen/guppyselection.3.gif
12) Nondisjunction:
https://image.slidesharecdn.com/ploidiespresentation-130422165803-phpapp01/95/nondisjunction-and-polyploidy-4-638.jpg?cb=1366650002
13) Polyploidy: ​http://vignette2.wikia.nocookie.net/uvmgg/images/b/b1/Polyploidy_gen.jpg/revision/latest?cb=20121129201101
14) Galapagos finches: ​https://myweb.rollins.edu/jsiry/darwin_finches.jpg