evolution final 2023

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110 Terms

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coincidental evolution hypothesis
human virulence is side effect of traits that are adaptive in the pathogen's normal habitat, for pathogens that do not usually have a human host
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short-sighted evolution
pathogens that live for many generations in single host aren't under selection for transmissibility
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trade-off evolution
damage to host is acceptable if it increases the chances of transmission to new hosts
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hemagglutinin
coat protein that helps virus bind to host cells, recognized by the host immune system
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pandemic strains
strains that are rapidly acquiring amino acid substitutions in sites under positive selection
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antigenic sites
parts of the protein of the virus that the immune system recognizes and remembers
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biological species concept
Species is a group of populations whose members have the potential to produce fertile offspring.
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phylogenetic species concept
defines a species as the smallest group of individuals that share a common ancestor
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morphological species concept
characterizes a species by body shape and other structural features
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lateral transfer species concept
species concept using bacteria and lateral gene transfer
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allopatric speciation
formation of species with physical isolation
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sympatric speciation
formation of new species in the same range- due to other barrier
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polyploidy
condition in which an organism has extra sets of chromosomes, can create rapid sympatric speciation
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vicariance
allopatric speciation that occurs when something in the environment separates organisms of the same species into separate groups
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dispersal
the movement of organisms from one place to another to create new species
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divergence
must occur to split species after isolation. reasons- adaptation to different habitats, assortative mating, more mutations
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reinforcement occurs
hybrids have reduced fitness
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hybrid zones
where geographic ranges of 2 species overlap
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disparity
morphological differences between taxa
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diversity
number of taxa and relationships between taxa
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morphospaces
ranges of trait values may be occupied or not, usually uneven- theoretical range is broader than observed range
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punctuated equilibrium
Pattern of evolution in which long stable periods are interrupted by brief periods of more rapid change
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phyletic gradualism
Species evolve by the accumulation of many small changes over a long time period
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adaptive radiation
rapid increase in disparity and diversity, driven by ecological opportunity or morphological innovation
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one island model
most gene flow is from continent to island. every individual that comes from mainland significantly impacts allele frequencies in island gene pool, way less impactful for mainland gene pool
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two island model
2 islands gene pools are more equally influence by each other
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genetic drift
describes the effect of random chance on allele frequencies. random
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sampling error
\= xbar - mu
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mu
actual mean
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xbar
sample mean
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founder effect
example of genetic drift, allele frequencies of those who migrate may not represent frequencies of population
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allopatric speciation
The formation of new species in populations that are geographically isolated from one another.
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random fixation
probability of an allele becoming fixed due to random chance is equal to its starting frequncy
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Loss of heterozygosity
happens on the way to fixation
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H g+1 means
heterozygosity in the next generation
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Hg+!
\= Hg (1- 1/2N)
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Fst means
fixation index, models loss of heterozygosity in isolated subpopulations
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Fst
\= (Ht-Hs)/Ht
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Ht
expected heterozygosity if entire population is in HWE, 2pq
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Hs
observed average heterozygosity across all subpopulations
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neutral loci
loci that are not under selection give better idea of when and how fast drift acts, good for molecular clock
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nonrandom mating
both sexual selection and inbreeding
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inbreeding
mating with genetic relatives, exacerbated by small population sizes, does not change allele frequencies but increases proportion of homozygotes
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inbreeding depression
result of increased homozygosity, deleterious recessive alleles are more likely to be expressed in this population
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linkage disequilibrium
When a pair of alleles from two loci are inherited together in the same gamete more/less often than random chance would expect, increased by inbreeding
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haplotype
multilocus genotype of a chromosome or gamete
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linked loci
physically proximate, less likely to be separated by crossing over during meiosis
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linkage equilibrium
genotype of a chromosome at one locus is independent of its genotype at the other locus
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D means
coefficient of linkage disequilibrium
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g
frequency of each haplotype in population
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D
\=gABgab - gAbgaB
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r
recombination rate, probability of crossing over
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sexual reproduction
reduces LD by crossing over during meiosis generating new haplotypes
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the older the mutation
the less closely linked it is to a certain haplotype
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common and strongly linked alleles
young and under positive selection
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mullers ratchet
describes accumulation of deleterious mutations in an asexual population and loss of genetic diversity to drift
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Quantitative traits
traits that show continuous variation ex. height, controlled by many different loci and environmental factors
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M
marker locus, helps identify loci that contribute to quantitative trait. if M predicts average phenotype, marker is linked to quantitative trait locus
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QTL
quantitative trait loci
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V
variance
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broad sense heritability
V genetic / V phenotypic
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V phenotypic
Vg + V environmental
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H
\= Vg/ Vg+Ve
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h^2
narrow sense heritability, equal to slope of least-squares regression line on plot of midparent and midoffspring trait values
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Vg\>Ve
trait is more heritable, identical twins will have more similar trait values than dizygotic twins
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t bar
mean trait value of population
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t star
mean trait value of individuals that reproduce
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selection differential
the difference between the mean of the group selected for reproduction and the mean of the entire population, s \= tstar-tbar
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selection gradient
plots relative fitness vs trait value, connects trait value to fitness
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breeders equation
calculates response to selection
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breeders equation actual
R \= h2s
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directional selection
changes the average trait value, moves curve over
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stablizing selection
decreases variance of trait without changing the average trait value
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adaptation
trait or integrated suite of traits that increases the fitness of its possessor, process in which a lineage evolves a trait that confers higher fitness
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determine what trait is for, show that individuals with the trait contribute more genes to future generations than individuals lacking it
how to test if trait is adaptive
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typically female
higher investing parent
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typically male
lower investing parent
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heavy investing parent limits
reproductive success limited by resources and time
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light investing parent limits
reproductive success limited by number of mates
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intersexual selection
sex with heavy investment in offspring is choosy about mating, one sex exacting selection on another
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intrasexual selection
sex with light investment in offspring will compete to mate, same sex exacting selection on each other
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intrasexual selection can lead to
adaptations for display or combat, sneaky behaviors
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sneaker males
"sneak" in and mate with females when the dominant or territorial male is not looking, do not fight or display. can be equally fit as competitive strategies
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sperm competition
competition between sperm of different males to fertilize eggs
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infanticide
individual killing the offspring of other males to increase own fitness
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preference
daughters preferred trait value often matches brothers measured trait value, increases likelihood of brothers mating success. "sexy sons hypothesis"
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why does preference exist
arbitrary, exploit sensory biases, increases resources available, signals that individual has good genes
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mutually beneficial behavior
benefits fitness of actor and recipient, ex. communal nesting
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selfish behavior
benefits actor at expense of recipient, ex. cane toad eggs eat each other
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altruistic behavior
benefits recipient at expense of the actor, ex. ground squirrel alarm calls
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spiteful behavior
harms both actor and recipient, ex. bacteria making toxins that kill other strains of their species
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direct fitness
Individual's own reproductive success
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indirect fitness
reproductive success of relatives
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inclusive fitness
direct fitness + indirect fitness
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Hamiltons rule
predicts when altruistic behavior will occur, B*r - C \> 0
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r
relatedness
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c
cost of direct fitness actor gives up
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b
benefit of direct fitness recipient gains
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relatedness definition
probability that shared allele is identical by descent
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identical by descent
shared allele is shared because was present in an ancestor