evolution Flashcards
what lead darwin to this observations of common ancestry
naturalistic observation; similar special geographically close to each other -> COMMON ANCESTRY
biogeography
in different parts of the world you observe different species but the
distribution of species; pattern darwin discovered
homologies
structures that have deep, underlying similarities between species; ex. forelimb bone structure
taxonomic group
a rank or group of organisms dloped on the basis of their fundamental characteristics, similarities and dissimilarities
transitional fossils
a fossil that exhibits characteristics of both ancestral and derived forms
nested structure
taxonomies structured as groups within groupse
evidence for common ancestry
All life uses the same molecules, DNA and RNA, to store genetic information; always with the
same nitrogenous bases (A, C, G, T, and U
polymorphic population
a population with genetic variation; stemming from mutation
Natural selection
genetic variants make an organism
better equipped for their environment will increase in frequency in populations over time; survival of the fittest
darwin’s 3 core ideas
- common ancestry
- if genetic variation is present populations will change
- natural selection; change in populations over time is adaptive
phylogenetic tree
a diagram that shows the evolutionary history of organisms, species, or genes
phylogenetic tree clade
a grouping of branches and tips that includes all the descendants of a single ancestral lineage
tree topology
representation of relationships between the clades in a tree; gives us
information about relationships
Tree Thinking
The ability to use the metaphor of a phylogenetic tree to convey accurate
evolutionary information
Speciation
Lineage splitting that ultimately leads to taxa that are classified as separate species
Taxon/ Taxa (plural)
a named group of biological organisms, often shown at the tips of a tree
Evidence of Common ancestry (4)
- fossil records
- biogeography
- homology
- classification (hierarchical nesting)
evolution of populations
*populations evolve over time
* populations evolve not individuals
*genetic composition of populations change over time
mutation frequency
spread of evolution of disease variants; higher frequency = most fit variant
natural selection
genetic variants that improve function, reproduction, survival that increase frequency
tree thinking
common ancestry depicted in tree form
reasons for split population lineages
- geographic/ climate changes/ rare dispersal events
what do split populations lead to
speciation
speciation
accumulation of differences -> no longer can interbreed and produce fertile offspring
*form incompatible -> divergence
clade
all descendants of ancestral lineage; all meet at 1 node/ common ancestor
sister lineages
lineages stemming from the same node
trait evolution
genetic changes in a population over time
* happens between nodes
true or false; all species are equally evolved
true!
homology
similarity of the structure, physiology, or development of different species of organisms based upon their descent from a common evolutionary ancestor
homologous spurs
part of tree where all species developed the same trait from the same common ancestor
types of non homology
convergence evolution and reversal
convergence evolution
nrelated species independently evolve similar traits
reversal
reactivation of lost genetic trait from many ancestors ago
parsimony
hypothesis that the best way to explain traits on a tree is the way with the fewest changes (least amount of gene develop/ lost)
parsimony assumption
loosing and gaining traits equally as likely
placisty of a population
genetic changes in population caused by environment; NOT evolution
ex. fertilizers -> plants grown taller
evolution only happens when… (2)
1) organisms differ genetically (not environmentally caused)
2) differences in reproductive success; dominant/ better trait more prevalent in next generation.
heritable variation
allele variation segregating in a population
segregating variation
variation neither lost nor fixed; variable within population
polygenic trait
trait controlled by multiple genes
environmental vriation
environmental factors that impact genetics; latitude, temp, elevation, developmental environment/ resources available
allele frequency of haploids
allele frequency = genotype frequency
allele frequency of diploids
A1 (p) = x+ y/2
A2 (q) = z + y/2
*3 possible genotypes
Hardy Weinberg
predict genotype frequencies from allele frequencies
- frequency of A1A1= p^2
- frequency of A2A2 = q^2
-frequency of A1A2= 2pq
hardy weinberg assumption
random mating
directional natural selection
when fitness is partially or completely dominant; eventually population’s genotype shift to the fittest trait
relative fitness
average number of offspring produced by 1 genotype relative to another
how is adaptive change supported
directional selection
trait dominance impact on frequency
dominant trait/mutation shows up in population more quickly than incomplete dominance and more than recessive
what decreases genetic variation
directional selection
what replenishes genetic variation
random genetic mutations
types of mutations
- substitution (silent/ synonymous or synonymous)
-insertion
-deletion
how is rate of mutation impacted by the “need” of a mutation (environmental problem/ need to adapt to environment)
they are independent factors! mutations are random
impact of majority of mutations
negative/ detrimental
genetic drift
change in genetic makeup of population by chance fluctuation.
what 2 factors lead to genetic drift
family size variation and mendelian segregation (only passing 1 allele each to offspring)
genetic drift and population size
*more dramatic in larger populations
*goes to fixation faster in smaller populations
fixation probability
higher probability -> goes to fixation faster
bottleneck effect
large population with lots of variation reduces in size and variation; takes a while to recover and reintroduce variation bc mutations are random and independent of need
how does genetic drift impact directional selection
small pop: reduces efficacy of directional selection
large pop: directional selection overcomes drift
recessive vs dominant diseases mutant alleles
higher rate of recessive disease alleles (hides in carriers); dominant disease mutation more lethal -> not passed on through natural selection.
overdominant selection
heterozygous is more fit than either homozygous; rare alleles most likely to be in heterozygote
balanced polymorphism
both alleles stay present in the pop because HT is the most favorable (over-domiant selection); occurs at locus with more than 1 allele
continuous trait
traits controlled by more than 1 gene; complex trait
heritability
the extent to which variation in a continuous trait has a genetic basis
correlation between parent and offspring trait: all variation is genetic
slope = 1
correlation between parent and offspring trait: all variation is environmental
slope = 0
strength of selection (s)
(mean of reproducing individuals) - (mean of pop)
response to selection (r)
(mean of offspring gen) - (mean of parent gen)
how to find r (response to selection)
h^2 * s
(heritability) * (strength of selection)
when does the offspring trait distribution differ from the parent trait distribution(shift)
when h^2 (heritability) is greater than 0
why is heritability hard to measure in/ overesterimated natural population
parent and offspring often have same environment -> hard to differentiate between heritability and environmental variation
heritability definition
percent of variability that is due to genetics
*not individual while population
eugenics movement
certain traits socially desirable and were assumed to be heritable -> only certain families with “desirable” traits could reproduce.
stabilizing selection
favors average individuals; reduces trait variation
disruptive selection
favors extreme individuals; increases trait variation
* to the extreme -> bimodal -> speciation
sexual selection
reduce/ does not effect individuals ability to survive BUT increases ability to reproduce/ mate
secondary sexual characteristics
one sex (usually males) develops trait to help reproductive/ mating success
ex. peacock tail feathers
sexual dimorphism
term used to describe the differences in appearance between the sexes of the same species
sexual dimorphism; monogamous vs polygamous species
monogamous: little sexual dimorphism
polygamous: more sexual dimorphism
why is male sexual dimorphism more extreme?
due to higher variance in reproductive output of male offspring
what does sexual selection drive the development of
male-male conflict and female choosiness
runaway sexual selection
feedback between female choice and male traits
why do trait distributions still have a bell curve shape (average favored) if the average has a lower fitness
random mating
assorted inbreeding
alike individuals more likely to mate with each other
-> leads to bimodal distribution -> speciation
Phylogenetic species concept
focus on evolutionary history (phylogenetic trees)
- species are taxa
- products of evolution
-sexual and asexual species
biological species concept
focuses on ability to successfully interbreed and produce fit offspring
- species are populations
-interbreeding throughout time
-only applies to sexual reproduction
what geographical model do species subgroups follow?
geographically discrete; distinct group 1 and group 2 spanning over geographical distance (small section for intermediate allele frequency)
speciation biology
evolution of reproductive incompatibility
reproductive incompatibility
behavioral, genetic, and/or physical differences that reinforce specificity and separation of 2 groups/ species
allopatry
groups that evolve in different places
sympatry
groups that evolved in the same place
does speciation mostly occur with allopatry or sympatry?
allopatry
conditions for sympatric speciation
strong disruptive selection AND assortative mating
complex traits
develop by direction selection of multiple little traits over long periods of time; ex. human eye
exaptation
traits that are beneficial in a species for one function but originated to fulfill a different function ; ex. bird feathers help with flight but originally helped with thermal insolation
founders effect
occurs when a small group of individuals separates from a larger population, resulting in a reduction in genetic diversity
3 origins of life
bacteria, archea, eukaryotes
evidence for common ancestry(4)
- same proteins/ 20 amino acids
- same genetic building blocks ; nucleotides
-same genetic machinery; ribosomes - same basic metabolic pathway; make ATP
LUCA
last universal common ancestor (of archaea, bacteria and eukaryotes)
*complex life forms before LUCA
differences between archaea and bacteria
bacteria are much more common and interact with the environment and other lifeforms much more
cyano bacteria and historical importance
bacteria that photosynthesises to produce oxygen; introduced oxygen to earths atmosphere so other life forms could occur
Endosymbiotic hypothesis
Hypothesis for how mitochondria and plastids formed in eukaryotes: formally prokaryotes with own DNA that were absorbed by and integrated into the eukaryote
Autogenous hypothesis
competing idea that mitochondria and plastids formed/ have their own DNA because double membrane organelle containing DNA splits into 22; nucleus and mitochondria/ plastid
Why exaggerated secondary sexual characteristics are more common in males than females?
Because males often differ greatly in mating success, selection more strongly favors traits that improve mating success (even if they lower survival).
What is fst
FST, or fixation index, is a statistic used to measure the degree of genetic differentiation between populations
Does evolution always require natural selection
While natural selection is a key mechanism driving evolution, evolution itself does not strictly require natural selection (drift can cause evolution)
what must be changing for evolution to be happening
allele frequency
inside out model; cell development
complex eukaryotic cells evolved by pushing out membrane protrusions from their original cell body, creating the internal compartments
outside in model; cell development
internal structures of a eukaryotic cell formed from plasma membrane folding inwards to create the nucleus and other organelles
