Evolution Flashcards
1
Q
Evidence of Common Ancestry
A
- Biogeography: patterns of similar-looking species living in certain parts of world (and absent from places they could potentially thrive)
- “Deep” Similarities/homologies: some species may not look alike but have very similar structures- similar structures may have different functions
- Transitional Fossils: fossils found carry a subset of traits of significant living groups
- Taxonomy: groups nested in groups
2
Q
What does common ancestry require
A
EVOLUTION
3
Q
What are the 3 big ideas of Evolution?
A
Common Ancestry, Populations Evolve, Natural Selection
4
Q
What is Natural Selection?
A
provides the direction, adaptations explained by natural selection. Better adaptation=live longer=reproduce and pass on traits
5
Q
What is the Main Idea of Common Ancestry?
A
unites all life, we all descended from a common ancestor
6
Q
Why do Populations evolve?
A
Populations evolve ( NOT INDIVIDUALS), as long as genetic variation (mutations) arise, the genetic
7
Q
What is Evolution?
A
change in a population (allele frequency) over time; chance driven by underlying genetic changes that are PERMANENT
8
Q
What is speciation/lineage-splitting
A
- Geographic isolation
- Isolation allows for genetic differentiation given environment + cannot reproduce with other groups
- Lineages isolated long enough lose the ability to interbreed
9
Q
How is relatedness determined?
A
by recency of a common ancestor
10
Q
What is a clade?
A
comprises ALL descendants of an ancestral lineage, all members of clade share a more recent ancestor than outside of clade
11
Q
What is a node?
A
when the descendant lineages 1st become genetically isolated
12
Q
On an evolutionary tree, where does character change (trait evolution) mainly occur?
A
on branches.
why? because evolution is an ongoing change, a lineage splitting event is just 1 instance of evolution (and represents a tiny fragment of time)
13
Q
Where does trait evolution occur?
A
happens along population lineages/branches and NOT tied to nodes or speciation or lineage-splitting events, modified, lost, or retained by descendants
14
Q
What is a taxonomy?
A
hierarchal structures that classify species based on traits
15
Q
What does homology mean?
A
similarity due to common ancestry; single trait evolves multiple times independently but look similar, can be traced to an evolutionary origin in a common ancestor
16
Q
What does non-homology mean?
A
similarity due to convergent adaptation. 2 types
- convergent evolution: trait with dif genes+ dif development of independent origins that function/look the same
- reversal: trait lost and then re-evolve again later on
17
Q
What is the principle of parsimony?
A
hypothesis on taxonomy which involves the fewest changes is MOST LIKELY true
18
Q
How do you assess confidence on a phylogenetic tree?
A
Bootstrapping generates hypothetical alternative data using current data. Creates “pseudoreplicate” data sets by sampling w/replacement from original data.
19
Q
What is an allele?
A
a particular variant of a gene in a population
20
Q
What is a locus?
A
place in genome where an allele is encoded
21
Q
What is a genotype?
A
genetic make-up of an organism
22
Q
What is a phenotype?
A
physical/behavioral/physiological characteristics of an individual
23
Q
What are the Hardy-Weinberg Laws?
A
- There is no mutation or migration
- Mating is random w/ respect to the alleles
- Alleles have equal fitness
- Population is infinitely large
24
Q
How can Evolution Happen?
A
One of the Hardy-Weinberg assumptions MUST be false.
- no mutation or migration
- mating is random with respect to the alleles
- alleles have equal fitness=selection
- population is infinitely large=genetic drift
25
What is directional natural selection?
one allele consistently enhances fitness or makes it stay the same(never reduce), results in the favored allele to increase in frequency, causes rapid fixation in a population, deleterious mutations driven extinct, acts on MANY loci
26
What is relative fitness?
relative fitness=average of offspring produced by genotype relative to other, offspring thus inherit higher fitness, fitness=environment dependent
27
What does directional selection do to a population?
constantly REMOVING genetic variation bc 1 allele favored over another and drive other allele to extinction
28
What replenishes genetic variation in a population?
mutations
29
What are the 2 scenarios for adaptive evolution?
1. Environment remains unchanged and new mutations arise to enhance fitness
2. Environment changes, altering relative fitness for pre-existing alleles
30
What is genetic drift?
random fluctuation of allele variants in a population, happens ALWAYS in finite populations, decreases genetic variation, acts on all LOCI compared to directional selection which only acts on 1, jaggedness on graph
31
Which allele will be "fixed" under drift?
initial frequency is the chance of an allele to go to fixation
ex: if the starting frequency of allele A is 0.5 then it has a 50% of going to fixation or a 50% chance of getting lost given that there is NO selection
32
How long until fixation happens?
- higher selection=faster fixation
- when no directional selection ONLY drift, population size determines the rate because small populations more EASILY lose variation faster (think about probability, more likely to get equal numbers of heads and tails in 100 rounds vs only 10)
- important to remember that directional selection overcomes genetic drift in LARGE populations and when favored allele has high initial frequency
33
What is selection?
heritable differences in fitness/phenotypes between genotypes in their fitness
34
What is overdominant selection?
heterozygotes most fit, tends toward equilibrium allele frequency, tends to keep allelic variation, w11w22
35
What is underdominant selection?
heterozygotes least fit, unstable equilibrium, favors whichever allele has a high frequency, rare alleles lost, w11>w12
36
What does genetic drift depend on (if no selection is present)?
population size, small populations tend to lose variations much quicker, w11=w12=w22 prob fixation=starting frequency
37
If genetic drift AND directional selection are present in a population which will win?
Directional selection will overcome G.D. in large populations + when favored allele is already @ high frequency, ineffective in small populations
38
How can we "look" for selection in a population?
look at genotype frequencies (compare actual population) to the HW assumptions calculations (expected)
39
Selection on Diploids
Not just directional, directional selection on many individual loci explains CONTINUOUS trait evolution
40
What are the explanations for continous variation?
1. Genetics:alleles at many loci affect ___, each allele has small effect ex:height
2. Environment (ex: nutrition)
3. Nature or nurture---always a bit of both
41
What is heritability (h^2)?
indicates fraction of population that is due to GENETICS
-all environment: h^2=0
-all genetic: h^2=1
tells us how much variation is available for selection
42
Response to selection
Response to selection=heritability x strength of selection
r=h^2 x s
r= response to selection (mean of offspring generation-mean of parental generation)
s= strength of selection (mean of reproducing individuals - mean of whole population)
43
What are the ways that selection can act on traits/phenotypes?
1. Directional: one extreme favored
2. Stabilizing: Average values are favored
3. Disruptive: both extremes are favored
44
Is stabilizing selection the same as overdominant selection?
NO!! Overdominant selection favors heterozygous GENOTYPES and tends to MAINTAIN allelic variation at ONE locus, while stabilizing selection favors PHENOTYPES near the mean and tends to REMOVE allelic variation @ MANY LOCI
45
What is disruptive selection?
favors phenotype near both extremes, increase variance/standard deviation of trait, tends to MAINTAIN allelic variation
46
What is stabilizing selection?
favors phenotypes near the mean, tends to remove allelic variation @ many loci, variance decreases, powerful agent of conservation
47
What is directional selection? (graph)
one extreme favored, population mean moves, variance decreases, favored allele fixed
48
What happens if variance/spread/standard deviation increases/decreases?
heritability (h^2) has direct relationship, so if variance decreases so does heritability
49
What is speciation? (Baum)
clades that are different enough to be recognized as distinct species, speciation requires lineage splitting + subsequent evolutionary divergence
50
What is allopatric speciation?
geographic separation usual driver
51
What is sympatric speciation?
speciation without geographic separation. If there is strong disruptive selection + assortative mating ( among 2 extremes, extreme 1 mates with extreme 1, 2 with 2) speciation can occur without allopatry
52
How does sympatric speciation work?
eventually selects for genetically linked genes that promote assortative mating based on trait
53
How do complex traits arise (trichromatic vision, wings, etc.)?
No planning ahead, often there are changes in a traits function
54
What is sexual selection?
kind of sexual selection for improved mating success (even at expense of survival); mostly in males--exaggerated secondary sexual characteristics; selection will favor until fitness offsets benefit from reproductive fitness
55
How does sexual selection function/what does it require?
requires pre-existing preference (usually female), selection favors males with trait=leads to more offspring, selection favors females that have a stronger preference to said trait=pickier females; mostly in polygamous species
56
What is altruism?
genetic tendency for organisms to help another (increasing their fitness) at their own fitness expense
57
What is group selection?
traits that improve the success of a multi-individual group may be favored even if there are disadvantages so a gene that enhances group fitness can increase in frequency EVEN IF it lowers individual fitness
58
What is the relationship between altruism and group selection?
groups compete, groups with more altruists do disproportionately better than groups with few
59
What are the levels of directional selection?
1. group:alleles that improve group fitness in the population tend to increase in frequency
2. individual (survivorship and sexual): alleles that improve individual fitness in the population tend to increase in frequency
3. gene: alleles that improve a gene fitness in a genome can increase in frequency (even if they lower organism/group fitness)
Some examples of gene selection/selfish genes include:
- allele gets into more than 1/2 of gametes
-gene makes extra copies of itself and inserts somewhere else
- a gene can get itself packaged in such a way to be transmitted to another organisms
60
Why is selection always among variants?
- selection within a population never favors traits because they are good for the species
- selection among individuals in a population will favor traits that are good for individuals that have the trait (even if bad for species)
- selection among clans in a population will favor traits that are good for the clans (even if bad for species)
61
What was the rate of evolution on the human lineage?
rate of neutral evolution not elevated but rapid evolution of morphological and behavioral traits, more directional vs. stabilizing selection
62
What is historical contingency?
life evolves due to mutations which are random/up to chance to make a trait ex: adaptations may not evolve sometimes (bc of chance) EVEN if trait would be beneficial ex: trichromatic vision
63
Why did human lineage diverge/what's the story?
other apes remained in same ecological niche, undergoing consistent stabilizing selection while humants underwent series of major ECOLOGICAL shifts undergoing consistent directional selection
64
What was the ecological change that humans diverged from apes?
Ancestral apes:forest-dwellers, arboreal (living in trees), fruit diet, foraging
Derived: savannah dwelling, largely terrestrial, meat diet, foraging + hunting
Ancestral lineage couldn't compete bc of drying climate and shrinking forest
65
When did bipedalism evolve?
3 Ma, drivers: looking for predators/prey, carrying throwing stuff, better cooling
66
What is the scavenger hypothesis?
using rocks to extract bone marrow, then group selection for ability to drive off competitors: run to get carcass, throw projectiles, work as team, resulted in gradual transition to true hunting
67
Are humans adapted to running?
Yes, we have long legs that lock and fully extend + foot arch, lighter frame, reduction in insulating body hair, increase in sweat glands are all traits that work together to allow humans for LONG distance running in HOT conditions
68
How come humans throw so well?
accumulation of existing traits, shoulder flexibility:locomotion, clasping hands:climbing, binocular vision:arboreality
69
What did selection in humans also improve in pre-existing traits?
fully opposable thumbs, expansion of the waist: allows the torso to rotate independently of hips, lowering of the shoulder:changes the orientation of many shoulder, which is crucial to storing E, reduced twisting of the upper arm bone:allow more E storage
70
When did modern humans migrate from Africa to the rest of world?
100,000 years ago
71
What additional traits did the transition to hunting select for?
bigger brains, new tools (ex:stone tools)
72
Why are modern humans genetically diverse but not subdivided?
lots of gene flow but LITTLE time to diverge, there are no biological races of humans as we are too homogenous
73
Why does genetic diversity decline with distance from Africa?
population migrated FROM Africa, went through genetic bottlenecks (population gets smaller=limits genetic diversity) + genetic variation, genetic variation is lost
74
What are the traits of ancestry in humans from oldest to youngest?
shoulder (arboreality/swinging on trees, bipedalism (first trait in humans, tools (little later after everything)
75
How did the evolution of trichromatism happen?
gain of function mutation, light-rector gene on X chromosome duplicated so there are two copies-specialized in red and green light, very complex
76
Why does the lack of trichcromatic vision in New World Monkeys not mean it is adaptive/advantageous?
historical contingency, New World Monkeys most likely would have trait if it arose earlier +selective benefit; sometimes waiting for a sequence of mutations hold up evolution, not just selection, lack of prehensile tail (complex) in Old World Monkeys most likely historical contingency
77
In contrast to trichromatism or a prehensile tail, why was evolving Vitamin C dependency easy?
loss of function genes-easier than gain of function, for particular trait loss is detrimental except in lineages that eat lots of fruit, mutations disrupted GULOP gene which synthesizes vitamin C
78
What is a pseudogene?
gene that is no longer creates a protein/ non-functional
79
Takeaways from historical contingency
1. some new traits arise commonly
- selection determines whether they evolve in lineage
2. some traits require rare mutations or sequences of improbably changes
- lineages that might benefit from trait don't evolve it
- historical contingency
80
Why did placental mammals outcompete others (like marsupials + monotremes)
1. egg-laying: offspring + parent vulnerable vs. live birth which produced more offspring
- -uncertain
81
Why did mammals outcompete other lineages?
1. higher metabolic rate
2. provisioning offspring
3. better hearing
4. better food handling
82
What is adaptive radiation?
radiation into many different ecological niches
| ex: land mammals, water mammals
83
Why did mammals invade land?
escaped from predators + new sources of food (plants+arthopods), there able to adapt limbs for locomotion + lungs to breathe
84
What are the 3 groups of animals
1. Sponges:2 layers,no symmetry
2. Cnidaria: 2 layers, radial symmetry, muscles and nerves
3. Bilateria:3 tissue layers, bilateral symmetry, muscles and nerves
