midterm #1 Flashcards
(70 cards)
1
Q
summary of natural selection
1.-4. + two inferences
A
- more offspring produced than needed
- most populations stay constant in size
- individuals differ
- individual traits are heritable
- > those with favourable traits tend to survive more often
- > they leave most offspring
2
Q
evolutionary synthesis
A
evolution =
Darwin’s natural selection +
Mendelian inheritance +
population genetics
3
Q
major eras
A
Archaean (till 2.5bya) Proterozoic (till 542mya) Paleozoic (till 251mya) Mesozoic (till 65.5mya) Cenozoic (till today)
4
Q
major events in early evolution
A
- origin of genetic code
- origin of cells (compartmentalization)
- 2 biochemical pathways: photosynthesis and aerobic respiration
- linear chromosomes (fast replication, larger genomes)
5
Q
multicellularity evolved…
A
… at least 4-5 times in eukaryotes
6
Q
multicellularity requires…
A
- gene regulation for cell differentiation
2. cell-to-cell communication for informing about position and differentiation state
7
Q
milestones in evolution of complex lives
A
- compartmentalized genomes
- eukaryotic cells
- multicellular organisms
8
Q
fossil record
A
- only in sedimentary rock
- only found in exposed or near-exposed strata
- <1% of once-living species known as fossils
9
Q
Archaean era (2)
A
- origin of cellular life
- photosynthesis & aerobic respiration
10
Q
Proterozoic era (3)
A
- eukaryotes
- multicellular life
- Ediacaran fauna
11
Q
Paleozoic era (4)
A
- Cambrian explosion
- land plants
- invertebrates (u.a. insects)
- vertebrates
12
Q
Mesozoic era
A
- dinosaurs and birds
- first mammals
13
Q
mammals’ evolution:
1) ancestors
2) innovations (3)
A
1) synapsid vertebrates
2) hair, mammary glands, middle ear bones
14
Q
evolution of hominins
A
- first primates: Cenozoic
- first hominins: Miocene Sahelanthropus
- earliest homo: Piocene/Pleistocene H. erectus
- H. sapiens: 200.000ya
15
Q
anagenesis
A
change within a lineage
16
Q
cladogenesis
A
splitting of lineages
17
Q
homology
A
similarity from common descent
18
Q
convergence
A
similarity from similar selection pressures
19
Q
homoplasy + 2 kinds
A
resemblance w/o common ancestry:
(1) convergence
(2) evolutionary reversal: evolution of a character back to its ancestral state (genetical distance but morphological closeness) - e.g. winglessness in insects
20
Q
reticulate evolution + 2 kinds
A
when branches on the tree rejoin
1) horizontal gene transfer (rare in eukaryotes, often in bacetria/archaea
(2) hybridization
21
Q
clade
A
monophyly/
all descendents of any one ancestor
22
Q
possible explanations for traits, apart from natural selection
A
- chromosome linkage
- genetic drift
- historical/phylogenetic factors (result of selection in the past)
23
Q
what indicates natural selection has been at work?
A
- correlation of trait frequency w/ environment
- variation in fitness with environment
- changes in trait frequencies between age classes or life stages
- responses to perturbation (of habitat)
24
Q
levels of selection
A
- individuals
- genes
- kin groups and populations
- species
25
genetic variation and environmental variation
genetic: variation in genotype (e.g. races)
environmental: variation in phenotype (e.g. seasonal plumage)
26
explanations for phenotypic variation
- genetics, epigenetics
- environmental differences (phenotypic plasticity to different environments)
- gen x envir interactions
27
human DNA
- <30% is transcribed
| - ca. 2% codes for actual proteins
28
microsatellites
short repeated DNA sequences
- one to many repetitions
- abundant in eukaryotes
29
unequal recombination
crossing-over when homologous sequences are not paired precisely
-> leads to insertions or deletions
30
aneuploidy
gain or loss of single chromosomes
31
polyploidy
gene duplication / gain of entire chromosome sets
- during meiosis: production of unreduced gametes
- during mitosis: failure of cytoplasmatic division
32
maternal effects
when phenotype of individual is an expression of the parent's genotype rather than the individual's genotype
(there's a causal influence of the maternal genotype or phenotype on the offspring phenotype)
33
types of chromosome rearrangements (3)
inversions:
- inverted gene order, during crossing-over
- > duplications/losses
reciprocal translocation:
- association of multiple chromosome pairs at recombination in meiosis
- exchange of chromosome segments between non-homologous chromosomes
- > duplications/losses
fissions and fusions:
- when one chromosome breaks into two
- when two non-homologous chromosomes are joined
34
absolute fitness R
R = mean number of progeny per parent
| if R = 1, genotype stays constant in numbers
35
relative fitness w
w = absolute fitness relative to maximum absolute fitness, between 0 and 1
shows increase/decline of genotype relative to other genotypes
36
R and w (gene fitness) and population size
R & w don't say anything about population increase or decrease itself: gene could be highest w in population, but have an R < 1
37
modes of natural selection (6)
single-locus traits:
(1) direcitonal selection: one of homozygotes has highest fitness
(2) overdominance/heterozygote advantage: heterozygote has highest fitness
(3) underdominance/heterozygote disadvantage: heterozygote has lowest fitness
continuously varying traits:
(4) stabilizing (same mean)
(5) diversifying/disrupting (often not symmetrical, so different mean)
(6) directional (different mean, Darwin's focus)
38
natural selection: temporal variation
short-term:
- different selection pressures on individuals within their lifetime
long-term:
- uniform selection pressures across lifetime, slowly changing over generations
39
natural selection: spatial variation
fine-grained:
- individuals encounter different patches of habitat
- depends also on mobility of individual
- favours generalists
coarse-grained:
- individual genotypes stay in single patches of habitat
- favours specialists/local adaptation
40
frequency-dependent selection
inverse: higher fitness for rare genotypes
(e. g. sex ratios, mating strains)
positive: higher fitness for common genotypes
(e. g. Müllerian mimicry in Heliconius butterflies)
41
Hardy-Weinberg equilibrium: assumptions
1) infinite population size
2) no natural selection (all individuals equally likely to reproduce)
3) no mutation
4) no gene flow or migration between populations
5) random mating
42
random genetic drift:
| direction/magnitude
direction: unpredictable
magnitude: predictable, depends on population size
43
random genetic drift:
| implications
short-term:
- random fluctuations in allele frequencies
long-term:
- loss/fixation of alleles (loss of variation within populations)
- genetic divergence between populations
- chance of fixation/loss is lower in larger populations
44
fixation of alleles
in alleles only affected by genetic drift, probability of becoming fixed is related to their initial frequency in the population
45
evidence of evolution (5)
- fossils
- embryological development
- homology
- molecular (DNA) similarities
- real-time observations of evolution
46
outgroup analysis
method to find which character state is ancestral and which is derived:
- taxa of interest are compared to related taxa outside the studied group
- take character states in outgroup taxa as ancestral
47
maximum parsimony (3 characteristics)
method to build phylogenetic trees:
- most likely tree is that with fewest evolutionary steps
- only shared characters indicate relationships
- all character changes are assumed equally likely to occur
48
maximum likelihood
method to build phylogenentic trees:
- weighs character changes in their probability of occurring
- takes branch length into account
49
general phylogenetic methods (3)
(1) explicitly phylogenetic/parsimony methods
- shared derived characters identfy groupings
- outgroups important in identifying shared derived characters
(2) distance methods
- based on overall resemblance
(3) molecular clocks
- DNA sequences change at more constant rate than morphologies
- can provide precise timelines for species, calibrated with fossils
- problem: rate of DNA change not always constant
50
segregation distortion
when selfish alleles at a locus are passed to a heterozygous individual's gametes more than 50% of time, allowing them to spread faster than other alleles
example: sex chromosomes, distorter alleles cause biased sex ratios
51
group selection
selection for traits costly to individual but beneficial for the group
- idea: populations with selfish genotypes have higher extinction rates than those with altruistic genotypes
- problem: within-population selection for selfish genotypes acts faster than group-level selection
52
species selection
selection based on correlation between a characteristic (e.g., body size) and rate of speciation or extinction
- changes proportion of species that have one character state rather than another over time
53
selection coefficient s
shows strength of selection favouring a beneficial allele
- is increase in chance of survival for each copy of the allele (e.g. s=0.5 is 50% increased chance of survival)
- determines rate of spread of beneficial alleles
54
effective population size Ne:
- description
- what used for
- factors affecting it (4)
size of an ideal population (where each individual reproduces and size is constant) that experiences genetic drift at the same rate as the population studied
- generally smaller than actual population size
- used to estimate strength of genetic drift: the smaller Ne, the stronger the drift
factors:
- variation in sex ratio
- n.s. affecting number of progeny
- overlapping generations
- fluctuation in population size
55
adaptive landscape
plots population's mean fitness against frequency of an allele
- shows adaptive peaks and valleys
- selection causes populations to evolve uphill on the landscape
- which peak is climbed depends on initial frequency
- in small popoulations, genetic drift can shift the population from one peak to another
56
inbreeding (non-random mating) and allele frequencies
- allele frequencies stay the same
| - increase in homozygote frequencies (offspring can inherit multiple copies of the same ancestral allele)
57
inbreeding depression
loss in fitness shown by offspring whose parents are
| close relatives compared with offspring whose parents are unrelated, due to greater chance of deleterious homozygosity
58
gene flow + implication
movement of genes between populations
- counteracts divergence among populations (greater homogeneity)
59
measuring gene flow (2)
- measure movement of individuals between birth and reproduction
- compare parent and offspring allele frequencies
60
gene flow over distance and time
- species with gene flow over long distances (migratory birds and fishes, wind-pollinated plants, passively dispersed marine organisms)
- timeline: short distances in one season add up to long distance over multiple generations
61
measuring genetic divergence among populations
Fst or Gst: proportion of observed genetic variation among populations
= 0 when populations have same alleles in same frequencies
= 1 when populations are fixed for different alleles
62
isolation-by-distance
divergence between pairs of populations is often correlated with distance between them
63
gene flow vs genetic drift
gene flow counteracts genetic drift bc increases effective population size
64
gene flow and natural selection (2)
1. reinforce one another when selection favours the same traits in different populations
2. counteract one another when selection is acting in opposite directions
(but: takes large amounts of gene flow to change effects of natural selection)
65
favouring low or high dispersal ability
high dispersal ability:
- colonizing species
- species in variable environments
- species subject to directional change in environment
low dispersal ability:
- species in stable environments
- species in isolated patches of favourable habitat
66
radiometric dating
- only possible on igneous rocks
| - use half-life of radioisotopes: proportion of daughter atoms in rock shows you how old the rock is
67
eukaryote characteristics (4)
- well-developed cytoskeleton
- linear chromosomes
- membrane-bound organelles
- present-day eukarya all descended from one single common ancestor
68
Cenozoic era
- cooling climate
- radiation of modern groups
- pollinating insects
- rise of hominins
69
uses of phylogenetic analyses (5)
- relationships of organisms
- ages of organisms and lineages
- ages and order of traits
- history of genes
- coevolution of species
70
founder effect: causes (2)
1) recent population crash
| 2) establishment of a new population from a small number of ancestors
