Population Genetics 1 Flashcards
facets of evolution (5)
- speciation and extinction
- origin and spread of new genetic variants
- gradual change over a long period of time
- rapid changes in response to changing conditions
- changes in the genetic pool
what is evolution
- CHANGE in the form/behaviour of organisms between generations
evolution
- described by Darwin
- descent with modification
evolution
- described by Futuyma and Kirkpatrick (4)
origin and alteration over generations of:
- ideas within society
- frequencies of genotypes within populations
- proportion of differentiated populations within species
- proportion of species with different traits within a lineage
how can evolutionary change occur? (2)
- chance bursts of reproduction, deaths or mutation
- natural selection
what does natural selection explain?
- explains how undirected change can improve the match between an organism and its environment
natural selection
- process whereby some individuals contribute more offspring to the next generation as a consequence of their carrying a trait(s) favourable to survival and reproduction
when does evolution by natural selection occur? (3)
occurs whenever
- individuals vary in some trait (VARIANCE)
- individuals with some trait values are more likely to live/reproduce (SELECTION)
- parents have offspring with similar trait values (HERITABILITY)
Aristotle (3)
- greek philosopher
- examined natural world for evidence of divine order
- created the Scale naturae (“Chain of Being”)
Scale naturae (“Chain of Being”) (3)
- hierarchical arrangement of forms
- species arranged linearly along a scale: god -> man -> mammals -> egg-laying animals -> insects -> plants -> non-living matter
- formed the basis for the western belief in the fixity of species, each of which has a typical form
Carolus Linnaeus (4)
- classified organisms according to binomial system, giving each a SPECIFIC and a GENERIC name (Genus species -> eg. Homo sapiens)
- proposed a nested system of relationships (as opposed to the Scale naturae)
- recognized fundamental difference between interbreeding (within species) and non-interbreeding organisms (non-interbreeding species)
- believed in balance of nature
what are the facets of the modernized Linnaean system? (7)
- generally know
- kingdom
- phylum
- class
- order
- family
- genus
- species
balance of nature (3)
- from Carolus Linnaeus
- each species has its place in a divine plan
- species would not chance or go extinct
- eventually acknowledged LIMITED formation of new species by hybridization
Comte de Buffon (2)
- beliefs
- believed Linnean hierarchy reflected common descent (dégéneration) with divergence over time
- believed that change only happened within families
common descent/dégéneration (3)
- from Comte de Buffon
- physical environment somehow changes organic particles
- new species form when animals migrate to new environments
- new environment then causes changes to the species
change only happens within families (2)
- from Comte de Buffon
- each family conforms to an internal mold
- species can change over time but are limited to their original mold at the family level
Erasmus Darwin (4)
- relation to Charles Darwin
- wrote…
- beliefs (2)
- Charles Darwins’ Grandfather
- Wrote Zoonomia/The Laws of Organic Life
- believed organisms constantly attempted to improve themselves by adapting to their environments (transformism/transmutation) but did not know the mechanism
- believed that all life consists of “one living filament” connecting all libing forms to a common ancestor
Jean-Baptiste Lamarck (3)
- theory of “transformism”, which was incorrect
- believed that at the base of hierarchy, “simple” organisms constantly arise by spontaneous generation
- suggested a mechanism for organic progression in Philosophie zoologique
theory of “transformism”
- organisms progress through a hierarchy of ever-more-advanced forms (almost a Scala naturae in reverse)
suggested mechanism for the theory of “transformism” (2)
- first law: use or disuse of a structure within a structure leads to its development or diminishment
- second law: these acquired characters can be passed on to offspring
suggested mechanism for the theory of “transformism” (2)
- example
- muscles shrink due to no use (diminish) OR muscles growing due to lots of us
- large/small muscles can be passed to offspring
Thomas Malthus (2)
- principle of overproduction: wrote “An Essay on the Principle of Population
- major of influence on Darwin and Wallace
principle of overproduction from “An Essay on the Principle of Population (3)
- from Thomas Malthus
- most organisms produce far more offspring than can possibly survive
- even when resources are plentiful, populations tend to grow geometrically until they outstrip their food supply
- poverty, disease, and famine are inevitable, leading to a “struggle for existence”
Charles Lyell (3)
- “uniformitarianism”
- his Principles of Geology was a major influence on Darwin and Wallace
- ideas on Earth was applied to his views on the living world
uniformitarianism (2)
- from Charles Lyell
- earth is subject to gradual and continuous change, but without progress or development
- earth remains in a steady state (slow building of volcanoes from earthquakes is also worn down by erosion at the same time)
Charles Darwin (3)
- life’s work: development of the theory of evolution by natural evolution
- used Lyell’s work to apply uniformitarianism to coral reef formation and developed appreciation for biogeographical patterns
- travelled around the world on The Voyage of the Beagle observing biodiversity and biogeography
biogeographical patterns (3)
- how organisms are arranged over space
- Darwin’s rhea
- giant tortoises and finches on the Galapagos Islands
niche
- similar combination of environment and vegetation that animals can occupy
biogeography (3)
- Darwin’s rhea
- considered why species such as ostrich, rhea and emu all inhabited similar niches differed when found on different continents
- noticed that two similar species often coexisted in a “boundary zone” where neither were better adapted than the other, and that these species must compete
- found that species were not fixed
biogeography
- giant tortoises
- on the Galapagos Islands, Darwin found giant tortoises that were distinct from each other even though they were on islands close together
biogeography (2)
- finches
- found species were closely related between islands
- determined that species change over time and fill different niches
natural selection (2) - from Charles Darwin
- recognized several critical facts about evolution by natural selection
- concluded that some variants will be preserved over time more than others and that the composition of populations must change over time
critical facts realized by Charles Darwin about natural selection (4)
- variability exists within species
- variant traits may be inherited
- Malthus’ Principle of Overproduction implies that many individuals must die or fail to reproduce
- therefore, individuals slightly better suited to their environment must be more likely to survive
how did Darwin explain speciation (2)
- as natural selection acts on geographically isolated populations, they become increasingly different from each other
- leads to formation of first varieties within species, then separate species, then genera…etc, in an ever-branching process
Alfred R. Wallace (3)
- profession and work
- who did he reference
- connection to Darwin
- English professional naturalist that travelled that world observing biodiversity and biogeography like Darwin
- read Lyell and Malthus’ work to discover natural selection and survival of the fittest
- sent letter to Darwin describing his independent discovery of natural selection
evolution made public (2)
- Darwin and Wallace’s views were co-presented at meetings in 1858
- Darwin published “ The Origin of Species by Means of Natural Selection” that revolutionized science due to depth and breadth
timeline of important figures of evolution (8)
- Aristotle
- Carolus Linneaus
- Comte de Buffon
- Erasmus Darwin
- Jean-Baptiste Lamarck
- Thomas Malthus
- Charles Lyell
- Charles Darwin and Alfred R. Wallace
why is the brief history of evolutionary thought dominated by white males
- many ideas and discoveries lost due to the denial of the privileges, education, and access to the records of history by non-white male demographics
why is diversity needed in the study of evolution (3)
- general reason
- dangers
- truth of evolution
- need diversity of education to completely understand whole diversity of evolution itself
- previous colonialism gave privilege to do research and publish books; created opportunity for biological racism that could incite harm to those targeted
- truth: we are all closely related no matter our skin colour and all living things are equally evolved
haploid
- one copy of each gene
diploid
- two copies of each gene
survival
- differential survival and reproduction of different entities
what are the steps in one generation cycle for a haploid organism (3)
- gamete union forms diploid phase
- meiosis forms haploid phase
- selection occurs during the haploid phase
how can we track two variant allele (A and a) frequencies after selection for a haploid organism? (3)
- generally know
after selection occurs in the haploid phase:
- freq A = W(A)*p[t]
- freq a = W(a)*q[t]
then the following occasion applies to find the frequencies of each allele; for the A allele:
W(A)p[t]/(W(A)p[t] + W(a)*q[t])
fitness (3)
- individuals haploids carrying varying alleles have different fitness
- average contribution per parent to the next generation including survival and reproduction
- symbol: W with subscript of allele
how can we track two variant allele (A and a) frequencies between the diploid -> haploid phase in haploid organisms? (3)
- fertilization brings alleles together (gamete union), followed by separation at meiosis; however there is no selection here so allele frequencies are expected to remain the same
- nothing perturbs frequency during this phase; therefore, no selection
- frequency remains the same from previous calculation, except that p[t] -> p[t+1]
does evolution by natural selection depend on the absolute or relative fitness values of alleles? explain (2)
- depends on their relative fitness values
- if the relative fitness values are the same, then the resulting change in frequency of evolutions will also be the same, even if the absolute fitness values change
how do we measure the fitness of each type of allele relative to W(a), relative to W(A), or relative to a standard W (3)
- divide both fitness values by W(a), making the W(a) fitness value 1
- divide both fitness values by W(A), making the W(A) fitness value 1
- divide both fitness values by a standard and set W
what happens to the allele A frequency if W(A) > W(a) during long term natural selection? (2)
- the frequency will converge to 1, p[t] -> 1
- “directional selection” favouring A
what happens to the allele A frequency if W(A) < W(a) during long term natural selection (2)
- the frequency will converge to 0, p[t] -> 0
- “directional selection” favouring a
how would you plot the change over time in the frequency of an allele A that increases fitness by 20%? (3)
- plot a graph with “frequency A” on the y-axis and “time” on the x-axis
- as W(A) is 1.2 and W(a) is 1, the frequency of allele A will converge to 1
- plot the line starting from ~0 and show that it eventually reaches 1 with an S-shaped curved line
how does variance affect the frequency change per generation within a haploid population? (4)
- affects
- how is this reflected on the plot
- high variance vs low variance
- section of formula affected
- more variability will increase the frequency change per generation
- this is reflected by a plot where the change is increasingly slow when the allele is rare and when it is common
- highest variability: p[t]=0.5 and q[t]=0.5; lowest variability occurs when one allele frequency is 1 and the other is 0
- in the per generation change formula: p[t]*q[t]
how does selection (difference in relative fitness values) affect the frequency change per generation within a haploid population? (3)
- affects
- how is this reflected on the plot
- section of formula affected
- higher difference in relative fitness values will create faster evolutionary change/more evolutionary change per generation
- plots with larger differences in relative fitness values will converge to 1 or 0 more quickly; the line will reach the top/bottom faster than a line with smaller difference
- W(A) - W(a)
how does selection (difference in relative fitness values) affect the frequency change per generation within a haploid population?
- not an effect; more of a condition: A-bearing parents with frequency p[t0 must pass A allele to offspring
what happens to the allele A frequency if W(A) = W(a) during long term natural selection (2)
- then the frequency of allele A will not change, p[t] remains at p[0]
- “neutral”
when considering the spread of a new beneficial allele (A) in a population of wildtype alleles (a), how do we measure fitness?
- measure fitness relative to wildtype using a selection coefficient
W(a) = 1
W(A) = 1 + s
selection coefficient (3)
- symbol
- defintion
- value limits
- symbol = s
- proportional increase in fitness caused by replacing a with A allele; larger |s| values will create larger evolutionary changes per generation
- can be positive or negative
how does the selection coefficient (s) change the # of generations it takes for allele A to rise from low frequency to high frequency (2)
- is s is 10 times smaller, it takes ~10 times longer (10x the amount of generations) to observe the same amount of frequency change
- is s=0.1 then it will take 100 generations; if s=0.01, then it will take 1000 generations
how does evolutionary change by natural selection affect the match between an organism and its environment?
- it increases the mean fitness of an organism
mean fitness of an organism
- symbol: Wbar[t]
- W(A)p[t] + W(a)q[t]
how does the mean fitness change across one generation in haploid organisms?
- the mean fitness rises (or stays the same) in the haploid model of evolutionary change cause the fit between organism and environment increases
if evolution were so easy and effective, why isn’t everything the same and perfect? (4)
- organisms vary
- environments vary
- the world is changing constantly
- evolution NOT by natural selection is also occurring
evolution NOT by natural selection (5)
- mutations arise
- chance plays a role
- sex and recombination alter
- alleles favoured for effects on some traits may affect other traits (pleiotropy and fitness trade-offs)
- neighbouring alleles in the genome can be dragged with selected alleles (hitchhiking)
