Flashcards
BIO Chapter 3a: Evolution I
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- 1BIO Chapter 3a: Evolution I...
- 2Defn of nat selectionNat selection → process in which indiv.s with certain inherited (favourable) traits tend to survive & reproduce at a higher rate than other indiv.s in an env.
- Organisms w favourable adaptations out-compete others in popn &displace them = fittest survive & reproduce thus differential reproduction. = over many gens, basic attributes (allele freq) changes in popn - 3(f) Define biological evoln as descent with modification & explain the link btwn micro & macro evoln. *defn of evolnEvolution → descent w modification from a common ancestor.
- modification→ evoln only occurs when there's CHANGES IN ALLELE FREQ over time within a popn (allele freq → chances of finding a particular allele of a gene within a popn)
- descent → evoln involve passing on of heritable genetic changes to the next gen
- common ancestor → present day species related through a common prehistoric ancestor that have changed & adapted over time - 4Defn - microevoln - macroevolnMicro → change in allel freq within a popn / species over SHORTER periods of time; doesn't give rise to new species
Macro → gradual changes in allele freqs over LONGER periods of time & may eventually give rise to new species (defining feature: speciation) - 5DIFF btwn micro & macro evolnMicro VS macro
Scale of changes in allele freq: small VS large
Time: Few gens VS thousands of gens
Level of changes: Within popn / species VS at/above level of species
Formation of a new species: no VS yes
Similarity btwn ancestors & descendants: descendant same as ancestor VS descendants diff from " as new species emerged
Evidence: from expt.s VS fossil records - 65 agents of evolutionary changes?1) Nat selectn
2) Disruption of gene flow
3) Genetic drift
4) Non-random mating
5) Mutation - 7(c) Explain role of nat selection in evoln. (1) Nat selectn - process? 1,2,3Nat selectn → results in survival of indiv.s w favourable adaptions / inherited char, to a particular env. Results in differential reproductive success in a popn & over many gens can change basic attributes of a popn.
(1) Overpdtn of offspring = exponential increase in popn size if offspring survive
(2) Constancy of numbers: most popns remain rel stable in size bcos only small fraction of offspring popn survives, matures & reproduces; majority die before repdtive age
(3) Struggle for survival: bcos comp for finite rsces & other factors (diseases/predators) limit their no.s - 8(a) Explain why variation is impt in nat selectn - process 4(4) Variation within popn → diffs btwn indivs of same species (due to diff alleles); allows nat selection to act on popn. Variation arises spontaneously & not dictated by needs of organisms to survive better in env. Some variants less adapted (unfav alleles) to survive in env, others better adapted.
Variation helps ensure perpetuation of species & safeguard species from extinction when env changes. Meiosis & sexual repro (random fusion of male & female gametes) is sig source of variation, thus offspring varied, BUT doesn't add new alleles to gene pool; just merely reshuffle existing alleles among indivs = diffs in pheno
Mutations introduce new alleles & enrich gene pool = new pheno = increased variation - 9- process 5(5) Survival of fittest by nat selection: when env changes (e.g. climate/new predator) occur, variation allow some indivs w selective adv (fav alleles) to survive & repdc more successfully than others. These survivors hv char.s that are selected for by env & help them adapt better to new env. Organisms which survive get a chance to produce viable, fertile offspring. Selection pressure → env factors, biotic & abiotic, acting upon survival & repdtive success of members of a popn
- 10-process 6,7(6) Like pdc like: surviving pdc offspring similar to themselves, adv char.s (det by fav alleles) more likely passed on to offspring. For evoln to occur, char.s must be heritable.
(7) Formatn of new species over long periods of time: unequal ability of indivs to survive & repdc = gradual change in popn. W each succeeding gen, proportion of indivs having adv char.s increases while those lacking decreases. Fav char, & thus fav geno. accumulate over time, changing allele freq
Over many gens, new species may form - 11(1) Type of nat selection - 3 diff ways of affect freq of a heritable trait in popn(1) Directional selection: pheno at 1 extreme end selected for. Once new mean phono coincides w new optimum env conditions, stabilising selection takes over (e.g. peppered moth - graph distorted to 1 direction)
(2) Disruptive selection: intermediate pheno selected against, favours indivs on both extreme ends of phenotypic range. (graph w dent in middle)
(3) Stabilising selection: extreme pheno selected against, favours more common int variants, doesn't promote evolutionary change but maintain phenotypic stability w a popn over time (graph slimmer) - 122(aii) Define niche [2]1. place/habitat where an organism lives;
2. and roles of an organism / interactions with other organisms in its habitat and environment e.g.
predator-prey relationship, decomposer etc.; (geog location =NOT niche) - 13(b) Explain, w e.g., how env factors act as forces of nat selection E.g. Peppered moth (& another: antibiotic resistant bacteria) -selection pressure: predatory birds2 varieties: lighter form & melanic (black) form (from spontaneous mutation NOT bcos industrial revoln)
- Initially, greater proportion of lighter form bcos well-camouflaged from predators on light coloured, lichen-covered barks = selective adv = selected for & increase in freq
- Industrial revoln: lichen killed & soot made barks darker. Lighter forms more visible & preyed = selected against = no declined. Darker camouflaged = selected for = increased in freq
- Thus, indivs w fav char.s more likely to survive & repdc, alleles that confer fav char.s passed on to next gen - 14E.g. Antibiotic resistance -defn antibiotic resistanceAntibiotic resistance → ability of microorganism to withstand effects of an antibiotic.
- 2 strains: anti-biot resistant (from mutatn) & non-resistant = variant exists natually
- Antibiotics kill most non-resistant bacteria = selected against
- Resistant bacteria = selective adv/selected for & more likely to survive & repdc, passing on allele for antibiotic resistance to subseq gens = freq increase in popn
Thus, differential repdtive success due to change in env. Selectn pressure = antibiotics - 15(2) Disruption of Gene FlowGene flow→ transfer of alleles from 1 popn to another, thru movement of fertile indiv.s or their gametes
- reduces diff in allele freqs btwn neighbouring popns.
- Disruption = changes in allele freq over time - 16(3) Genetic DriftGenetic drift → a change in allele freq due to chance events - allele ends up lost from original gene pool from indiscriminate random event. (alleles lost from RANDOM indivs NOT due to disadv pheno)
- Reduce genetic variation thru losses of alleles.
(i) Founder's effect: a few random indivs from larger popn become pioneers of newly isolated popn & not likely to carry all alleles present in original popn. Continuous breeding within new popn = rare alleles become common
(ii) Bottleneck effect: catastrophic event cause drastic reduction in popn thus reduction in allele freq & elimination of alleles in random nature. Few, random surviving indivs constitute random genetic sample of original popn, some alleles over/under-represented. - 17(4) Non-random mating- Preferentially choose mates, no random mixing of gametes
- E.g. one inherited pheno improves chances of successful mating (sexual selection) = allele more prominent in next gen - 18(5) MutationMutation → random change in organism's DNA & source of new alleles
- to impact evoln, must occur in gametes = inherited
- doesn't act directly on allele freq, ONLY agent that introduces new alleles, such that evo forces can then change allele freq - 19(d) Explain why popn is the smallest unit that can evolve. - defn oponA popn → grp of interbreeding indivs belonging to same species & sharing common geographic area
Evoln → measure of changes in allele freq.'s in a popn over successive gens
- LT effects of nat selection are at level of gene & popn, not indiv. Survivors interbreed to pass on fav alleles to next gen. Over time, these indivs contribute to allele freq changes that can be measured in a popn. Time needed to measure allele freq changes & allele freq cannot be measured in 1 indiv, but in a popn
- Although nat selection occurs through interactions btwn indiv organisms & their env, it's the collective genetic response of the popn that det survival of the species & formation of new species. - 20(h) Explain various concepts of the species (biological, ecological, morphological, genetic & phylogenetic concepts) - bio defnBio defn → species is a grp of organisms capable of interbreeding & pacing fertile, viable offspring & are repdtively isolated from other such grps.
Adv: See if organism can interbreed to pdc fertile (ability to pdc next gen), viable (can live) offspring
Disadv: Cannot be applied to asexually repcing organisms & extinct ones; and plants that are capable of polyploidy - 21Tutorial Q2.(ai) Define species [3]1. a group of organisms of the same species are capable of interbreeding* and producing fertile, viable offspring*;
2. are reproductively isolated* from other species;
3. have a common gene pool and same chromosome number; (thus can form gametes that can be fertilised = fertile, viable offspring) (e.g. if 1 gamete 3 chr & 2nd gamete 2 chr = viable but not fertile offspring bcos meiosis can't occur, chr cannot pair up)
4. usually have similar morphological, physiological and behavioural features; - 22- genetic defnGenetic defn → grp of genetically compatible interbreeding organisms in a natural popn that is genetically isolated from other such grps. (genetically isolated but NOT repdtively isolated)
- genetic isolation → 2 genomes diverge to point where they are genetically distance & evolve independently of one another
- BUT if mated can still pdc fertile viable offspring (e.g. polar bears & grizzly bears) - 23(c) Explain how new species are formed wrt geog isolation (allopatric speciation) & behavioural/physiological isolation within same geographical location (sympatric speciation) * defn speciation - requirementSpeciation → process whereby 1 or more new species arise from previously existing species
-Disruption of gene flow req for speciation & occur via isolating mechanisms - 24Allopatric speciation- a popn in 1 geographic area
- members geog-isolated due to phy barrier
- disruption of gene flow
- Evolutionary changes occur independently within each sub-popn i.e. diff genetic changes from accumulations of mutations, changes in allele freq thru genetic drift & nat selection occurred within each sub-popn
- over time, new species form - 25Sympatric speciation- a popn in 1 geographic area
- members not grog-isolated BUT reproductive barrier emerges that isolates a subset of a popn from the remainder of the popn in same area.
- disruption of gene flow
- Evolutionary changes occur independently within each sub-popn i.e. diff genetic changes from accumulations of mutations, changes in allele freq thru genetic drift & nat selection occurred within each sub-popn
- over time, new species form - 26E.g. Allopatric speciation - Finches- Ancestral popn strayed from South American mainland to one of Galapagos Islands & colonised other islands
- Sub-popns geog isolated in various islands & no interbreeding = disruption of gene flow
- divided popns exposed to diff envs in diff islands & under diff selection pressures
- Since there's variation among popns, fav chars selected for & unfav chars selected against resulting in changes in allele freq.'s
- Evo changes occur independently within each sub-popn i.e.diff genetic changes from...
- over many successive gens, each sub-popn became genetically distinct species, they are repdtively isolated & unable to interbreed to form fertile, viable offspring.
- Islands favour speciation bcos geog isolated from mainland & diff env conditions.
*Adaptive radiation → evolutionary pattern in which theres a rapid increase in no of species paced from a common ancestor upon introduction into new envs - 27Sympatric speciation - physiological isolation E.g. Palms- Physiological isolation → mating btwn indivs of diff sub-popns existing in same geog area not possible due to unique physiology
- physio diff = repdtive barrier = block gene flow
- 2 soil types: Older volcanic soil & younger calcareous soils. Normally grow on volcanic soil, some palms started growing on calcareous soil = flowering time diff as a physic response to growing on diff soil.
- prevent interbreeding btwn 2 sub popns growing in same area
- disruption of gene flow = evo changes occurring independently within each sub-popn i.e....
- Since there's variation within popn, fav chars selected for, unfav char against in 2 diff env
- Each sub-popn → genetically distinct species & repdtively isolated - 28Behavioural isolation e.g. Eastern & Western MeadowlarkBehavioural isolation → mating btwn certain indiv.s of popn existing in same geog area doesn't occur due to unique mating rituals & preferences
Behavioural diff = repdtive barrier = block gene flow
- some members of ancestral popn developed new call
- new bird call became more distinct over gens , birds began to distinguish btwn the 2 calls & mate preferentially w members w same call
-disruption of gene flow = evo changes occur independently within each sub-popn i.e....
- Over many gens, sub-popn = genetically distinct species, eastern meadowlark & western meadowlark; repdtively isolated - 29types of repdtive barriers- prezygotic mechanism (prevents mating / fertilisation)
- postzygotic mechanism (causes zygotic fatality or prevents hybrids from developing into fertile adults)
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- A level BIOLOGY (BIO CORE IDEA 4: BIOLOGICAL EVOLUTION) FlashCards sobre BIO Chapter 3a: Evolution I, criado por ws_ 149 em 17-03-2018.
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