Evolution Flashcards
1
Q
What is evolution?
A
The change in the properties of groups of organisms over the course of generations that is transmitted via genetic material from one generation to the next
2
Q
What is essentialism? - Plato and Aristotle.
A
Essence as a transcendent ideal form, variation is accidental imperfection.
3
Q
What is special creation?
A
Christian philosophy where each species has been created individually by God in the same form as today.
4
Q
What did Galen do?
A
Dissected human corpses to study human anatomy. Previously knowledge was based on animal dissections.
5
Q
Contributors to historical knowledge:
A
Comparative anatomy (Galen). Observation. Fossils - old earth, ancient life. Linnaeus - nested hierarchies rather than scala naturae. Lamarck. Uniformitarianism. Ecology of humans - geometric human growth + arithmetic food growth = crisis point = selection pressure. Natural selection.
6
Q
Lamarckian evolution:
A
Species change over time driven by use and inheritance. Evolution from simplicity to complexity.
Species originated individually by spontaneous generation. Hierarchy as species originated at different times and differ in age.
7
Q
What is uniformitarianism?
A
Lyell, Hutton - the same processes operated in the past as today. Geology should be explained by causes that can be observed today.
8
Q
When was the HMS Beagle’s voyage?
A
27.12.1831 - 2.10.1836.
Visited Africa, South America, Australia and more.
9
Q
What are Darwin’s finches?
A
Finches from different islands form 13 closely related species. Beaks adapted for different food sources on the islands. Darwin suggested they were once one species.
10
Q
Evolutionary theory: Darwin and Wallace.
A
- The characteristics of organisms change over time.
- Species have diverged from a common ancestor - life is all one family tree (common descent).
- Differences between organisms evolved incrementally (gradualism).
- Evolution occurs by changes in the proportions of individuals in a population with different inherited characteristics (population change).
- Changes in proportions are caused by differences in the individuals’ abilities to survive and reproduce - adaptations (natural selection).
11
Q
Differences between Darwin and Lamarck:
A
Darwin: Common ancestry. Based on random variation. Evolution towards better fitness and survival. Extinction. Lamarck: No common ancestry. Depends on use vs disuse of traits. Evolution towards increased complexity. No extinction.
12
Q
Darwin and Wallace did not explain hereditary variation. What was the prevailing theory?
A
Blending inheritance - parents characteristics are mixed and offspring are intermediates between their parents features. Reduces variation.
13
Q
What did Mendel do?
A
Discovered particulate inheritance by hybridising peas. Discrete genes, dominant and recessive. Characteristics inherited as particles which are unchanged from one generation to the next. Variation continues.
14
Q
What is a species?
A
A group of individuals that reproduce primarily among themselves.
15
Q
What is the modern synthesis?
A
Reconciled Darwin’s theory of natural selection with genetics. Acquired characteristics are not inherited (except epigenetics), variation is amplified by recombination, evolutionary change entails a change in proportions of individuals in a population with different genotypes by random drift/natural selection. Speciation.
16
Q
What causes adaptive evolution?
A
Mutation and natural selection.
17
Q
What is speciation?
A
The origin of 2 or more species from a single common ancestor which usually occurs by the genetic differentiation of geographically segregated populations.
18
Q
How old is the Earth?
A
4.5 billion years old based on radiometric dating (1/2 life = 0.7 billion years).
19
Q
How does most of the evolution of DNA sequences occur?
A
By genetic drift (rather than natural selection). Molecular clock.
20
Q
What are small, medium and large mutations?
A
Small: nucleotide sized.
Medium: sub-chromosome sized.
Large: chromosome and karyotype sized.
21
Q
What are the ultimate sources of variation?
A
Mutation and recombination.
22
Q
What is genetic variation?
A
Differences in the genetic sequence inherited.
23
Q
What is environmental variation?
A
Differences in the environment of an individual.
24
Q
What is developmental noise?
A
Random events at the molecular level.
25
What are the sources of variation in phenotypic character?
Genetic variation, environmental variation and developmental noise.
26
How does the environment affect development or expression of features?
Enzyme induction, environmental sex determination and maternal effects.
27
What are small mutations?
Point mutations (may cause new protein sequences), insertions and deletions (frameshifts - often produce non-functional proteins).
28
What are medium mutations?
Inversions and horizontal gene transfer (foreign DNA, entirely novel functions).
29
What are large mutations?
Translocations - exchange of segments from non-homologous chromosomes, may be balanced (euploid) or unbalanced (aneuploid), metacentric/acrocentric chromosomes.
Karyoptic changes - polyploidisation in plants).
30
What is the problem with polyploidisation in plants?
Barrier to gene flow and speciation. 15-30% of speciation accompanied by ploidy increase in vascular plants.
31
When do mutations mostly occur?
During DNA replication in cell division. Some changes are not repaired by DNA polymerase and proof reading enzymes.
32
Why do mutations in somatic cells have no evolutionary consequences?
They are not transmitted to the next generation (in organisms where the germ line is segregated from the soma in early development).
33
How is the rate of a mutation measured?
The number of independent origins per gene copy per generation.
34
What is the average mutation rate as measured by the patience method (waiting for mutations to occur at specific loci)?
10^-5 to 10^-6 mutations per gamete per generation.
35
What is the indirect method of estimating mutation rate?
Comparing the number of base pair differences between homologous genes of different species with the time since they diverged (known from fossils). 10^-9 per sexual generation (eukaryotes).
36
What is the direct method of estimating mutation rate?
Next generation sequencing.
37
How many base pairs are in the human genome?
7x10^9.
38
Are mutation rates constant?
No, they vary between genes and chromosome regions. They are also affected by mutagens.
39
Mutations occur at random but:
1. All mutations are not equally likely (developmental constraints).
2. All loci are not equally mutable (differences in rates).
3. Environmental factors influence mutation rates.
40
Why is mutation not equivalent to evolution?
Most mutations do not become fixed (substitutions) - where the mutation is carried by nearly the whole population due to natural selection or genetic drift.
41
How does recombination contribute to variation?
Reciprocal recombination does not generate new alleles, but creates new combinations of alleles at different loci.
Non reciprocal recombinations cause tandem duplications. Subsequent mutations can then lead to new proteins.
42
What is genotypic frequency?
The proportion of a population with a certain genotype.
43
How is genotypic frequency measured (fr(AA))?
Number of individuals with the genotype (AA) / the number of individuals in the population.
44
What is allelic frequency?
The proportion of a population that carries a certain allele.
45
How is allelic frequency measured (fr(A))?
(The number of homozygous individuals (AA) + 1/2 x the number of heterozygous individuals (Aa)) / the total number of individuals in the population.
46
fr(AA) + fr(Aa) + fr(aa) = D + H + R = ?
1.
47
Fr(A) + fr (a) = p + q = ?
1.
48
What is the wild type allele?
The most common allele at the locus.
49
What are the assumptions of an ideal population that would produce a Hardy Weinberg equilibrium?
1. No genetic drift (infinite size).
2. No natural selection (reproductive success independent of genotype at the locus).
3. Random mating.
4. No mutation.
5. No migration.
50
If a locus is in Hardy Weinberg equilibrium, what will the genotype frequencies be after one generation of random mating (remaining constant in subsequent generations)?
p^2:2pq:q^2.
51
If evolution is occurring, will allele frequencies be in HW equilibrium?
No. One of the assumptions has been violated and force(s) for allele frequency change are in effect.
52
How is expected genotype frequency calculated?
By estimating p and q for the population.
53
How can we tell if a genotype is in HW equilibrium?
Compare the expected and observed frequencies.
54
F (heterozygotes) = ?
(He-Ho)/He.
| Change in heterozygosity from HW equilibrium.
55
Human vs ape anatomy: skull.
Humans have larger foreheads, smaller brow bridges, less prognathous jaws, smaller canines and a chin.
56
What are our closest relatives?
Chimpanzees.
57
Human vs ape anatomy: brain.
Humans have larger brains with well developed frontal lobes, language areas (Broca's and Wernicke's) and motor strips.
58
Human vs ape anatomy: hands.
Humans have straight fingers and longer and opposable thumbs for more precise gripping (rather than climbing/swinging).
59
What are features of bipedalism?
1. Non-opposable great toe.
2. Femurs angled inward and knees closer together.
3. Different insertions of gluteal muscles.
4. Broader, bowl-shaped pelvis.
5. S-shaped vertebral column.
6. Head fixed in altered position.
60
Which species represents the early phase of human evolution?
Sahelanthropus -Ardipithecus.
61
Describe ardipithecus.
Bipedal with reduced canines, frequently arboreal. C/E Africa, 4-7ma. Still ape like.
62
What does ardipithecus show about human evolution?
That bipedalism and canine reduction happened before brain enlargement and tool use (move from arboreal lifestyle).
63
Adaptive significance of bipedalism:
1. Frees hands/arms for carrying tools, weapons, food/water, infants...
2. Allows travel between separate trees to feed.
3. Allows feeding from tall bushes (reaching) or on grass seeds (dexterity).
4. Allows humans to see over tall grasses.
5. Better thermoregulation.
6. Aquatic life - swimming.
64
What is the second phase of human evolution?
The Australopithecine.
65
Describe the Australopithecine phase.
4-2ma, Africa (widespread), further canine reduction and still partly arboreal. Many fossils and at least 8 species (Australopithecus), signs of early tool use? Radiations driven by African aridity?
66
Describe the human phase.
2-0ma, global spread, several species (Homo habilis, erectus, heidelbergensis, neanderthalensis and sapiens), small canine reduction and encephalisation, rarely arboreal, wider dietary range and behavioural complexity. Human anatomy.
67
What are the 3 constant selection regimes?
1. Directional selection.
2. Stabilising selection.
3. Diversifying selection.
68
What is directional selection?
Where an advantageous allele replaces a disadvantageous one.
Eg warfarin in rats.
Number of generations this takes depends on:
1. Selection coefficient (s).
2. Initial allele frequencies.
3. Degree of dominance (h).
69
What is stabilising selection?
Selection favours heterozygotes. More Aa than AA or aa. Eg sickle cell anaemia in Africa.
70
What is diversifying selection?
Heterozygotes selected against. More AA and aa than Aa.
Eg beak size in seed cracking finches, small and large beak sizes good for different sized seeds. Disruptive selection maintains 2 beak sizes while intermediate sizes are selected against.
71
What happens when the fitness of a genotype is different in different contexts?
1. Temporal fluctuation - changes from one generation to next.
2. Spatial variation - different in 2 different places.
May maintain variation though because on average, change in frequency may be 0 (positive somewhere/time and negative others).
72
The change in F (inbreeding coefficient) over generations depends on what?
The relatedness of the average pair of mates.
| More closely related pairs = faster rate of increase of F.
73
What is inbreeding depression?
A reduction in fitness seen in inbred populations due to increasing homozygosity and recessive disorders.
74
What is an adaptation?
A characteristic that enhances the survival or reproduction of organisms that have it relative to the alternative (ancestral) characteristic.
An outcome of natural selection.
75
When might a trait not be an adaptation?
1. The trait may be a necessary consequence of physics/chemistry.
2. The trait may have evolved through genetic drift.
3. The trait may have evolved because it is linked with another trait that is adaptive (pleiotropy).
4. The trait may be a consequence of phylogenetic history (remnant, vestigial eg wet-induced wrinkled fingers would have enhanced grip on wet surfaces for primates).
76
What are exaptions?
When a previous adaptation or non-adaptation is co-opted for a new use.
Eg keas using beaks to open cars or blue tits to get into milk bottles.
77
What are the hierarchical levels of natural selection?
1. Gene level.
2. Individual level.
3. Group level.
78
What is genetic selection?
When genes are transmitted at a higher rate than the rest of the genome and are not advantageous to the individual.
Eg. fruit flies that are carriers of the SD mutant gene (heterozygotes) show segregation distortion so that 95% of sperm carry the mutant gene. This lowers the fertility of the individual and the mutation is lethal in homozygotes so no benefit at the individual level - gene level adaptation.
79
What is group selection?
Traits might evolve that benefit the population but not the individual.
80
What is non-enforced cooperation?
Where cooperative behaviour evolves because it is advantageous to the individual, e.g. joining a flock/herd.
81
What is enforced cooperation?
Manipulation and punishment:
Where the donor is manipulated or coerced into helping the recipient, e.g. cuckoos (brood parasites).
OR
Reciprocity:
Where it is advantageous for the donor to help the recipient because the recipient may reciprocate in the future, eg. vampire bats.
82
What is the ESS?
Evolutionary stable strategy - the phenotype which can't be bested when played against itself.
83
What is game theory?
Optimisation when the fitness of a trait depends on the state of the rest of the population, so fitness is a function of the individual's trait as well the traits of others.
84
What is inclusive fitness?
Where a recipient receives fitness indirectly from the direct fitness strategy of an actor.
Direct + indirect = inclusive.
Kin selection - traits are selected because they help relatives, even at detriment to individual.
85
What must green beard genes need to do?
1. Produce phenotype - signal to others.
2. Recognise signal in others.
3. Direct cooperation towards others with the phenotype.
Eg. fire ant workers with b allele at the GP-9 locus decapitate prospective queens if they do not have the allele. Recognition is by odour.
86
How to discriminate kin?
1. Treat those in your home as kin (would usually be offspring/siblings).
2. Treat those you grew up with as kin - ground squirrels.
3. Learn to recognise phenotypes of closely related individuals and use that to infer relatedness of unfamiliar individuals, e.g. smell.
4. Green beard genes - no learning, programmed recognition.
87
What is parental care?
Any investment by the parent in an individual offspring that increases the offspring's chance of survival, but at the cost of investment in other offspring (either within or between broods).
Quality vs quantity.
88
What are the 3 types of family conflict?
1. Sexual conflict - between parents over how much care each should give.
2. Sibling conflict - how much care each should demand.
3. Parent - offspring conflict - care supply vs. demand. Optimum care for parent to give is lower than optimum for offspring to receive.
89
What is intragenomic conflict?
When genes promote their own spread at a faster rate than other parts of the genome, it can create a context where there is selection for genes at other loci to suppress their effects - genetic conflict.
90
What is genomic imprinting?
The asymmetric expression of genes with different parental origin - maternally/paternally biased, expressed or silenced.
91
What is a monophyletic group (clade)?
An assemblage including the common ancestor and all its descendants.
92
What is a paraphyletic group?
An assemblage including the common ancestor but not all of its descendants. Eg birds have the same common ancestor as reptiles but are not classed as reptiles.
93
What is a polyphyletic group?
An assemblage that doesn't include the common ancestor of the group.
94
What are polytomies?
Nodes in phylogenies with more than 2 descendants - a "pitchfork".
Usually means not enough data to determine how the groups are actually related, but can sometimes mean multiple speciations took place at the same time (e.g. cichlids).
95
What are plesiomorphic and apomorphic states?
The original characteristic for the lineage and the changed one.
Eg relatives and ancestors of snakes have legs (plesiomorphic) but snakes don't (apomorphic).
96
How does the placenta facilitate the transfer of resources from the mother to the offspring?
1. Placental trophoblasts invade the maternal myometrium and modify maternal spiral arteries to increase blood flow to the placenta (conflict = maternal arteries become more convoluted to increase resistance). Paternally expressed IGF2 influences the extent of placental invasion and therefore maternal artery modification.
2. The placenta secretes human placental lactogen, which causes insulin resistance in the maternal cells. This results in elevated blood glucose levels in the mother and increased transfer of resources to the foetus. Can cause gestational diabetes. Pi PLAGL and Mi LOT1 and HYMA1 also linked.
97
What causes Prader-Willi and Angelman syndromes?
Prader-Willi = deletion in a gene on paternal ch 15.
Pre-weaning: reduced activity and poor suckling.
Post-weaning: insatiable appetite and obesity.
Angelman = deletion in maternal version of gene.
Increased activity and prolonged duration of suckling.
98
What are the 3 basic assumptions in cladistics?
1. Change in characteristics occurs in lineages over time.
2. All organisms are descended from a common ancestor.
3. There is a branching pattern of lineage splitting (dividing into 2 groups).
99
What are homologous and analogous characteristics?
Homologous: Characteristics that are similar because they were inherited from a common ancestor - useful for constructing phylogenies.
Analogous:
Characteristics that are similar, but due to convergent evolution (dorsal fins in sharks and dolphins) - not useful for phylogenies.
100
How to construct a tree?
1. Choose taxa.
2. Choose characteristic(s) and determine state(s) for each taxon.
3. Determine polarity of characteristic(s) - i.e. original and changed.
4. Group taxa by synapomorphies.
5. Work out conflicts - simplest explanation (fewest evolutionary changes).
101
What are synapomorphies and symplesiomorphies?
Synapomorphies:
Changed character states shared by at least 2 taxa.
Symplesiomorphies:
Original character states shared by at least 2 taxa.
102
What is the biological species concept?
Species are groups of actually or potentially interbreeding populations, which are reproductively isolated from other such groups.
103
What are the problems with the biological species concept?
1. Can't use for asexually reproducing organisms eg bacteria.
2. Don't know whether ancestral populations would be able to interbreed with modern day descendants.
3. Genetically distinct populations can sometimes interbreed to produce hybrids (may be semispecies), eg grey oak and Gambels oak.
4. Different populations may interbreed in some locations but not others, eg spotted and collared towhees.
104
What are barriers to gene flow?
```
Pre-mating:
1. Temporal.
2. Spatial.
3. Behavioural.
Post-mating/pre-zygotic:
1. Mechanical.
2. Gamete incompatibility.
Post-zygotic:
1. Hybrids do not survive.
2. Hybrids are sterile.
3. Hybrids are less competitive than either parent.
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