evolution Flashcards
where does trait evolution occur on a phylogenetic tree?
internodes
tips
summations over their evolutionary history
relationship between relatedness and similarity
-similarity does not determine relatedness
-the number of trait changes does not determine relatedness
separate ancestry
the alternative hypothesis to common ancestry, which proposes that each living taxon has an independent origin
rate of trait evolution
-about the same for all branches
-the expected number of changes from the root will be the same for all living tips
-more nodes does not equal more trait changes
-all living species are equally “evolved”
exceptions to the nesting pattern within the common ancestry model
-a trait might evolve independently a few times
-a trait may evolve and later on be lost on one or more lineages
homologous trait
trait shared in separate species that derives from the same evolutionary origin
non-homologous trait
trait shared in separate species that derives from different evolutionary origins through convergent evolution
principle of parsimony
the hypothesis that invokes the fewest changes is most likely to be true; this reasoning works so long as the trait is one that evolves relatively rarely
occam’s razor
similar to parsimony; the simplest explanation for an observation is most likely the correct one
are trait gains or losses more likely?
equally likely
convergent evolution
the same trait evolves separately in more than one lineage; although they appear similar, these traits are not homologous
reversal
an ancestral trait was lost and then re-evolved along a lineage; makes the trait non-homologous
ancestral trait reconstruction
if we know where changes occurred, we also know ancestral states
evolution’s 3 big ideas
1) common ancestry unites all life
-diverse living species descend
from common ancestors
2) populations evolve
-the genetic composition of
populations changes over time
3) natural selection provides direction
-adaptations are explained by
natural selection (and related
processes)
phylogenetic tree
a branching diagram used to represent evolutionary relationships and relatedness between different organisms based on their common ancestry
root
the base of a tree, representing the common ancestral lineage of all taxa in the tree
branch
the lines that make up a tree diagram, which represent population lineages
taxon (plural= taxa)
a named group of biological organisms, often shown at the tips of a tree
lineage splitting/speciation
splitting of a population into genetically separate populations that no longer have gene flow; the origin of multiple species from a few ancestral species
node
branching point on a tree diagram, which represents lineage splitting
reasons for lineage splitting
-geographic changes
-climate changes
-rare dispersal events
clade
all descendants of an ancestral lineage
sister clade/lineage
lineages or clades from the same node
tree topology
a list of all clades a tree contains; stable to pruning
relatedness
recency of common ancestry
biogeography
the geographic distribution of living organisms
common ancestry
the concept that if you trace back the lineages of living species far enough in time, those species will converge to a shared ancestor
evidence for common ancestry
-biogeography
~similar species occur near one
another
-fossil record
~transitional forms in temporal
sequence
-homology
~surprising similarities among
organisms
-classification
~hierarchical nesting of biological
taxa
homology
traits whose similarities are explained by common ancestry
transitional fossil
fossil taxa that have some, but not all, of the derived traits of a living group
nested hierarchy/classification
a pattern of groups nested within groups (without overlaps) as seen in taxonomies
polymorphism
the existence of multiple variants within a population
evolution
the change in frequency of genetic variants within a population; changes in allele frequency of a population over time
fixation
the loss of all variants except one from a population
natural selection
the tendency for genetic variants that enhance fitness to go to fixation and variants that reduce fitness to be lost from a population, making the population better suited to its environment over time
plasticity
changes caused by the environment that do not have a genetic basis
locus
a place in the genome where alleles reside; in diploids, each individual has two alleles per locus
allele frequency
in a population, the proportion of all alleles at a locus that are of a particular type; changes in allele frequency over time causes evolution
heritable variation
allelic variation is segregating in a population
what determines phenotype of an individual?
the alleles they carry at many loci and the environment
hardy-weinberg assumptions
-no mutation
-no migration
-no selection
-mating is random with respect to the alleles
hardy-weinberg law
assuming assumptions hold:
-homozygote frequencies are the
square of the corresponding allele
frequency (p^2 or q^2)
-heterozygote frequencies are twice
the product of their allele
frequencies (2pq)
deviations from hardy-weinberg assumptions that cause evolution
-selection: alleles do not have equal fitness
-genetic drift: population is not infinitely large
probability that an allele becomes fixed under genetic drift
equal to that allele’s frequency
genetic drift
random change in allele frequencies in a population over time
genetic bottleneck
phenomenon in which a population lineage shrinks to a small size for a period, causing that population to lose genetic variation; occurred during the expansion of human populations around the world
how does directional selection affect genetic drift?
directional selection biases the genetic drift towards the favored allele
when can genetic drift overcome directional selection?
when the population is small and the allele being selected starts at a low frequency
directional selection
occurs when genotypes differ in fitness and one allele is favored; eventually the beneficial allele is expected to become fixed in the population
relative fitness
the fitness of a given genotype divided by the fitness of a reference genotype, which relative fitness is assigned to be 1.0
beneficial mutation
a new allele that enhances the fitness of organisms
deleterious mutation
a new allele that decreased organismal fitness
neutral mutation
a new allele with neither a beneficial nor deleterious effect
over-dominant selection
heterozygotes have the highest fitness; acts on a few genetic disease loci
under-dominant selection
homozygotes have the highest fitness
trans-specific polymorphism
a set of alleles that are shared between closely related species; they arose before speciation and were maintained as polymorphisms; can be explained by over-dominant selection
continuous trait
a trait that is characterized by values on a continuous scale, rather than being controlled by a single locus
disruptive selection
selection that favors trait values at both ends of the trait value distribution; mean stays the same, variance increases
heritability (h^2)
the fraction of the variation in a population that can be explained by genetics
response to selection (r)
the amount the mean trait value in a population changes after one generation
stabilizing selection
selection that disfavors extreme trait values and favors trait values towards the center of the trait value distribution; mean stays the same, variance decreases
standard deviation
square root of variance
variance
a measure of the spread of distribution of trait values in a population (the sum of the squared deviations from the mean value)
strength of selection
mean of the reproducing individuals minus the mean of the whole population
exaptation
the phenomenon in which a trait that evolved for one function is currently used for a different function
exaggerated secondary sexual characteristics
dramatic traits in an organism that lower the organism’s viability but evolve because they are favored by sexual selection
sexual selection
directional selection in which the selective pressure is on mating, instead of on survivorship
runaway sexual selection
the phenomenon in which secondary sexual traits become exaggerated due to feedback between male traits and female preferences
polygamy
the phenomenon in which one male can mate with many females
monogamy
the phenomenon in which one male mates with one female
altruism
actions (or tendencies to act) that result in the organism exhibiting the behavior lowering its own fitness while increasing the fitness of other organisms within its population
group selection
in a population composed of subgroups that vary in their frequency of altruistic individuals, subgroups with more altruists leave more offspring than ones with primarily non-altruists
biological species concept
the view that species are defined by the ability of their members to reproduce with one another and to be unable to reproduce with members of other species
phylogenetic species concept
the view that species are clades (monophyletic groups), like other in the taxonomic hierarchy, that biologists have chosen to assign to the species rank for practical reasons
clinal variation
gradual changes in traits as a function of geographical separation
discrete variation
genetic variation among geographically separated populations, where each population contains genetically similar individuals
Fst
ranges from 0 to 1 with higher values indicating more genetic variation between subpopulations (0.25 is sufficient to recognize biological races)
speciation
the splitting of ancestral species into descendant species
allopatric speciation
speciation driven by geographical isolation
assortative mating
the phenomenon in which individual organisms tend to mate with other organisms with trait values like their own
sympatric speciation
speciation without geographical isolation, driven by disruptive selection and assortative mating within a population; rare
extrinsic reproductive isolation
the phenomenon in which two organisms are unable to reproduce due to geographic isolation
intrinsic reproductive isolation
the phenomenon in which two organisms are no longer able to reproduce, even when they are allowed to encounter one another
oxygenic photosynthesis
the reduction of carbon dioxide to organic molecules using light energy in which water is the electron donor and oxygen gas is released
anoxygenic photosynthesis
the reduction of carbon dioxide to organic molecules using light energy in which something other than water is the electron donor and oxygen gas is not released
great oxidation event
the evolution of cyanobacteria to perform oxygenic photosynthesis and oxygenate the atmosphere
common traits of cellular life
-proteins and L-amino acids
-genetic molecules
-genetic system
-metabolic system
last universal common ancestor (LUCA)
-last living thing ancestral to all known life
-had all features shared by archaea, bacteria, and eukaryotes including a metabolism and genetic system that contained ribosomes, DNA, and proteins
bacteria
prokaryotic cells that perform critical functions for our biosphere including cycling carbon, photosynthesis, and chemosynthesis; can be parasitic or mutualistic; metabolically diverse
cyanobacteria
only lineage to evolve oxygenic photosynthesis; can be single-celled or form filaments of many cells
archaea
metabolically diverse; membranes are made of ether-linked isoprenoids
prokaryotic cells
lack membrane bound organelles; consist of bacteria and archea
organelle
membrane-bound compartment of a eukaryotic cell
endomembrane system
other membrane-bound organelles, including the endoplasmic reticulum, golgi apparatus, and secretory vesicles
endosymbiosis
the phenomenon in which a prokaryotic cell comes to live and divide within a host cell
evidence for endosymbiosis as the origin of the mitochondria
-bacteria and mitochondria both contain a circular genome and ribosomes
-mitochondria perform biochemical reactions in a similar manner to some free-living alphaproteobacteria
-mitochondria arise from the growth and division of existing mitochondria
-phylogenetic analysis of genes in the mitochondrial genome
autogenous hypothesis for eukaryotes
the theory that mitochondria and nuclei both evolved within the same eukaryotic lineage
outside-in model
the theory for the development of eukaryotes that starts with the production of vesicles within the cytoplasm by internalization
inside-out model
the theory for the development of eukaryotic internal compartments that suggests that the outer plasma membrane of a prokaryotic ancestor was pushed outward and ultimately fused to create the cytoplasm and plasma membrane of eukaryotes
asgard archaea
prokaryotes more closely related to eukaryotes than any other organism; produce extracellular protrusions, including long filamentous ones; provides support for the inside-out theory
mitochondria
derived from alphaproteobacteria
plastids
derived from cyanobacteria
characteristics of hominids
-bedding down
-diurnal
-complex social systems capable of coordinated actions as a group
-problem solving skills
differences between humans and other hominids
-opposable thumbs
-less body hair
-larger brain
-shorter gut
-physically weaker
-fully bipedal
-better at throwing
-better at problem solving
-true language
diurnal
the characteristic of being active during the day
hominid
great ape clade; of the primate clade; sister clade is gibbons
arboreal
tree-dwelling
hominin
all modern and extinct humans and their immediate ancestors
hypotheses of bipedality origin
1) by being upright, it is easier to look for prey and predators in the grassy savannas
2) if you are upright, your hands are free to do actions such as carrying and throwing
3) in a vertical position in a hot savanna, an organism intercepts less sun and is better at cooling
4) for long distances, hominins are more efficient at locomoting than other hominids (not supported)
introgression
the transfer of genetic information between species
admixture
the mating of two individuals from genetically distinct groups
evolutionary events that changed the planet
1) oxygenic photosynthesis (cyanobacteria)
2) invasion of land (plants)
3) agriculture and technology (humans)
anthropoids
monkeys; mainly frugivores
frugivory
diet of fruits and succulent-like produce from plants
