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Alevel Biology > Evolution > Flashcards

Evolution Flashcards

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1
Q

Define evolution

A

descent with modification from a common ancestor

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2
Q

Explain the link between micro and macro evolution

A

Microevolution may eventually lead to macroevolution, given enough time

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3
Q

Compare micro and macro evolution

A
  • S: occurs due to change in allele freq in popu over successive gen
  • Scale of change in allele freq
  • *Time period
  • Level of changes
  • *New species formed?
  • Similarity between ancestors and descendants
  • Evidence
  • *Examples
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4
Q

Explain why the population is the smallest unit that can evolve

A
  • Population: group of interbreeding individuals of the same species
  • (micro)Evo: change in allele freq in a population over successive generations
  • Change in allele freq can only be measured in a population over successive generations over time (beyond lifespan of an indiv), and not in an indiv
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5
Q

Explain the role of NS in evolution

A
  1. Overproduction of offspring
  2. But due to competition for limited resources, predators and diff selection pressure, many fail to survive
    3, Hence size of most popu stay relatively constant
  3. Variation exists within popu, due to different alleles and hence phenotypic differences. It is the raw material for NS to act on
  4. When env changes, indivs that are better adapted have favourable alleles coding for favourable traits w selective advantage→ selected for→ survive and reproduce more successfully to produce fertile, viable offspring
    - selection pressure
  5. Passing on favourable alleles cpding for favourable traits to the offspring
  6. Microevo occurs: change in allele freq, where in/decrease in freq of favourable/unfavourable allele.
    Over thousands of gen, reproductive isolation occurs, new species formed through speciation. Macroevo occurs.
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6
Q

Describe 2 examples of NS

A
  • Peppered moths: lighter form and melanic form via spontaneous mutation
  • more lighter forms: camouflage on lichen-covered trees–> escape predation–> selective advantage, selected for
  • industrialisation–> lichen killed, dark coloured bark exposed.
  • Lighter form selected against: easily spotted, vulnerable to predation by birds (selection pressure)
  • Melanic form has a selective advantage due to melanic allele→ selected for: camouflage on dark tree bark to escape predation→ survive, reproduce→ pass on melanic allele to offspring
  • freq of melanic allele ↑, ↓ freq of alleles coding for light form→ microevo occured
  • now most in melanic form
  • Bac: antibiotic resistant due to mutation, non-resistant
  • Change in env & selection pressure by antibiotics to kill bac
  • Non-resistant bac selected against
  • Antibiotic resistant strains have a selective advantage due to allele for resistance, selected for: survive antibiotics→ survive, reproduce, passing on alleles for antibiotic resistance
  • freq of antibiotic resistant allele ↑
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7
Q

What is direction selection + example?

A

phenotype at one extreme selected for→ favours initially relatively rare indivs

E.g. peppered moths, antibiotic resistance in bac

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8
Q

What is disruptive selection + example?

A

intermediate phenotypes select against→ favours indivs on both extremes of phenotypic range
E.g. Snails: pale shells selected for in dry grasslands, dark broad bands selected for in areas w leaf litter

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9
Q

What is stabilising selection + example?

A

Extreme phenotypes select against→ favour more common intermediates
E.g. Infant birth weight: babies heavier/lighter than optimum at a selective disadvantage (higher mortality)

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10
Q

What is gene flow?

A

the transfer of alleles from one population to another, due to: movement of fertile indivs/gametes→ interbreed→ tends to ↓ differences in allele freq between populations

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11
Q

What is the criteria for genetic drift?

A

chance event, alleles lost from random indivs, small population→ Δ allele freq; reduce genetic variation

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12
Q

Describe the founder’s effect

A

a few, random indivs pioneers of a new population + not likely to carry all alleles present in original population→ new population is small and reproductively isolated
⇒ Δ in allele freq: some alleles over-represented/under-represented

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13
Q

Describe the bottleneck effect

A

catastrophic event→ drastic reduction in population→ few, random surviving indivs constitute a random genetic sample of original population
⇒ Δ in allele freq: some alleles over-represented/under-represented

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14
Q

Describe mutation’s role in evolution

A
  • Mutations during gamete formation→ inherited by offspring
  • Source of new alleles→ ↑ genetic variation→ phenotypic variation for NS to act on
  • Favourable mutation→ phenotypes hv selective advantage, selected for → ↑ freq of favourable allele
  • Disadvantageous mutation→ phenotype selected against→ ↓ freq of disadvantages allele in population
  • ⇒ Microevolution occurs (Δ in allele freq)
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15
Q

Describe the biological concept of the species

A

Species is a group of organisms that interbreed to produce fertile, viable offspring + reproductively isolated from other such grps

  • Share common gene pool, same chromosome no.
  • Usually similar morphological, physiological and behavioural features
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16
Q

What is an advantage of the biological concept of species?

A

Organisms studied can be interbred to see if they produce fertile, viable offspring

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17
Q

Describe the genetic concept of species

A

Species is a grp of genetically compatible interbreeding organisms, that’s genetically isolated from other such grps
- Diff genetic species are genetically isolated: genetically distinct→ evolve & undergo genetic changes independently of each other→ changes in behaviour/type of pheromones associated with species recognition→ don’t interbreed in nature

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18
Q

What is an advantage and disadvantage of the genetic concept of species

A

A: Genetic data from mitochondrial & nuclear DNA to identify species is unambiguous in deducing evolutionary rs
DA: Tech needed to study DNA seq is relatively expensive

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19
Q

Describe the ecological concept of species

A

species is a grp of organisms sharing same ecological niche
- Differences in species due to differences in ecological resources they depend on. If species can no longer occupy a particular niche, it would be considered a new species

20
Q

Describe an advantage and disadvantage of the ecological concept of species

A

A: Every organism has a niche→ identity of species is unambiguous
DA: Unrelated species may hv similar niches

21
Q

Describe the morphological concept of species

A

species is a grp of organisms sharing similar body shape, size and other structural features
- Can be applied to all organisms

22
Q

Describe advantage and disadvantages of morphological concept of species

A

A: morphological features easily studied

DA:

  • Difficult to determine degree of difference needed to indicate separate species & what struc features shld be used to distinguish the differences
  • Superficially similar but hv diff evolutionary origins (convergent evo)
  • Large morphological differences can exist within a species e.g. domestic dogs
23
Q

Describe the phylogenetic concept of species

A

Species is smallest grp of organisms that share a most recent common ancestor & can be distinguished from other such grps

24
Q

What is an advantage and disadvantage of the phylogenetic concept of species

A

A: Avoid mistakenly classifying organisms based on superficial morphological traits as traits comapred are based on common ancestry/homology
DA: Accuracy dependent on availability, diversity and accuracy of source data

25
Q

Describe allopatric speciation

A
  1. Ancestral population in one geographic area
  2. Ancestral population separated into 2 sub-population due to physical barrier→ geographically isolated
  3. Barrier prevents interbreeding between sub-populations→ gene flow between 2 subpopulations disrupted (A)
  4. Subpopulations exposed to diff selection pressures in their diff env/niches. (Explain NS here) Variation in each sub-population→ those better adapted to env have selective advantage due to favourable traits, selected for→ survive, reproduce and pass on alleles to next gen→ ↑ freq of favourable alleles in population
  5. Evolutionary changes & different genetic changes occur independently within each sub-population: (A) accumulation of mutations, genetic drift, NS→ micro-evo: Δ in allele freq
  6. Over thousands of gen, each subpopulation become distinct species, which are reproductively isolated and unable to interbreed to form fertile, viable offspring. Hence, new species form from allopatric speciation and macroevo has occurred
26
Q

Give 2 examples of allopatric speciation

A

E.g. Ancestral porkfish population split into 2 sub-populations by formation of a land bridge that separated Caribbean sea from Pacific ocean
–> Caribbean porkfish vs Panamic porkfish
E.g. ancestral population of Darwin’s finches colonised parts of the Galapagos islands→ sub-populations separated by islands: sea between islands and between island and mainland
–> adaptive radiation of Darwin’s finches on Galapagos Islands

27
Q

Describe sympatric speciation

A
  1. Ancestral population in one geographic area
  2. Ancestral population separated into 2 sub-populations due to reproductive barrier: physiological or behavioural isolation
  3. Barrier prevents interbreeding between sub-populations→ gene flow between 2 subpopulations disrupted (A)
  4. Subpopulations exposed to diff selection pressures in their diff env/niches. (Explain NS here) Variation in each sub-population→ those better adapted to env have selective advantage due to favourable traits, selected for→ survive, reproduce and pass on alleles to next gen→ ↑ allele freq of favourable alleles in populatio (except behavioural isolation?)
  5. Evolutionary changes & different genetic changes occur independently within each sub-population (evolve independently): (A) accumulation of mutations, genetic drift, NS→ micro-evo: Δ in allele freq
  6. Over thousands of gen, each subpopulation become distinct species, which are reproductively isolated and unable to interbreed to form fertile, viable offspring. Hence, new species form from sympatric speciation and macroevo has occurred
28
Q

Give 2 examples of sympatric speciation

A

E.g. (physiological) Ancestral palms on Lord Howe island grown on volcanic soil & calcareous soil in close proximity→ diff flowering time
–> 2 diff species of palms: Howea forsteriana and Howea belmoreana
E.g. (behavioural) In ancestral population of meadowlark, some developed a new bird call such that birds tend to mate preferentially w members of the same call
–> eastern and western meadowlark, although regions they are found overlap

29
Q

Explain the ways in which islands favour the formation of new species/role of islands in speciation/Explain why islands often gave many unique species of life not found anywhere else

A
  • Are geographically isolated: surrounding water acts as a physical barrier to prevent interbreeding→ disrupt gene flow
  • Diff islands hv diff envs→ many niches for species to fill (adaptive radiation) e.g.: clayey soil type, availability of water/shade, plant types different
  • Diff selection pressures
  • Variation→ those with favourable traits and better adapted have a selective advantage, selected for→ survive, reproduce pass on alleles to next gen→ ↑ freq of favourable alleles
  • Different sub-popu evolv independently of each other, allele freq changed: accumulate diff mutations, genetic drift and NS
  • Over thousands of gen, each population on the different islands became reproductively isolated→ cannot interbreed to produce viable, fertile offspring→ new species formed through allopatric speciation (i.e. macroevolution occurs)
30
Q

What is a phylogenetic tree?

A

show evo rs and history; more closely related organisms are grouped closer tgt

31
Q

Compare biological classification/taxonomy and phylogeny

A 
Basis of grouping organisms
System of organising organisms
How species are presented
Nature of charcteristics 
Types of characteristics used
Strengths and weakness
Inference of speciation events, common ancestors & relationships
32
Q

How to construct phylogenetic tree via mlc homology?

A

Choose homologous gene common to the grp of organisms being compared and is derived from common ancestor e.g. cytochroms C gene
Amplify gene using PCR and then sequence the gene
Carry out seq alignment using computer programme
Compare similarities & differences & generate evo tree

33
Q

What is the importance/basis of mlc methods?

A

All living organisms contain nucleic acids in which evolutionary changes are captured. More closely related species → greater no. of similar nt seq→ greater no. of similar aa seq

34
Q

What are the advantages of molecular methods in classifying organisms?

A
  1. Objective, as mlc character states are unambiguous
  2. Quantitative: mlc data can be converted into numerical, amendabel to statistical analysis. Degree of relatedness can be quantified and inferred by calculating nt differences between species
  3. Can compare all organisms which share common genes, even remotely related organisms
  4. Can compare organisms that are morphologically indistinguishable due to convergent evolution/are closely related
  5. Changes in nt seq accumulate over time with clockwork regularity→ can estimate the time of speciation
  6. Mlc differences may not be reflected as a morphological difference while small genetic differences may result in a major phenotypic difference. Hence mlc data does not underestimate nor exaggerate differences.
  7. Methods offer a large set of characters to be studied quickly
  8. Data can be accessed from electronic databases for comparative study & classification of all life
  9. Specimens need not be complete or alive for comparative analysis, can use living and dead tissue
35
Q

Describe how mitochondrial DNA can be used to determine degree of relatedness between two different species.

A
  • Unlike nuclear DNA, no recombination, crossing over in mtDNA from parent to offspring→ change in DNA seq solely due to accumulation of mutations over time at a regular rate→ estimate timing of speciation
  • Faster mutation rate→ useful for comparing indivs within a species/species that are closely related as you require discernible differences between the DNA of organisms being compared
36
Q

Describe how homology differs from analogy

A

Analogous characteristics: similar characteristics due to convergent evo, which is when 2 species that don’t share a recent common ancestor independently evolve similar traits (similar selection pressure)

Homologous characteristics/homology: underlying anatomical & molecular similarities due to common ancestry
- Characteristics in ancestral organism developed into different forms due to NS, as they faced diff env conditions (Define what “descent with modification” means) w diff selection pressure

37
Q

Explain how anatomical homology (pentadactyl limb) support Darwin’s theory of evolution by NS

A

Same arrangement of bones but superficially look different and have diff functions (e.g. swimming in whales, flying in bats)
Pentadactyl limb of common ancestor was modified: NS→ diff forms to suit their specialised functions/envs

38
Q

Explain how anatomical homology (vestigial structures) support Darwin’s theory of evolution by NS

A
  • Vestigial struc: homologous struc that are greatly reduced in size, or have little to no function
  • Organisms w vestigial struc share common ancetrsy in which struc is still functional
  • Hind limbs in whales no longer beneficial to whales which swim→ reduced to small bones ⇒ presence suggests common ancestry w tetrapods
  • Appendix in humans reduced from the cecum of its primate ancestors which was involved in digestion of plant material⇒ presence suggests common ancestry w primates
39
Q

Explain how molecular homologies support Darwin’s theory of evolution by NS

A

Molecular homology: similarity in DNA, RNA & aa seq as they share common ancestor

  • Important enough that every organism possesses them, they carry out same function in diff organisms.
  • Seq are conserved & found → suggest common ancestry
  • Nt seq in ancestral genes modified due to accumulation of mutations, selection pressure favour some over others
  • Greater seq similarity between homologous genes→ more closely related
  • Homologous genes e.g. cytochrome C (mtDNA), p53 protein, haemoglobin
40
Q

Explain how fossils including transitional fossils support Darwin’s theory of evolution by NS

A
  • Determine how old it is by radioactive/carbon dating techniques
  • When compared across strata, they show an ordered seq of succession of organisms (in deeper strata = existed earlier) & how homologous struc were modified through time, from common ancestor to present descendant through a series of transitional forms, driven by NS
  • Horse fossils: shows ordered seq of progression in terms of lengthening of limbs, toe reduction and increase in tooth size over time that coincided w the change in env from dense forests to open grasslands. Through NS, these adaptations transformed ancestral horse into modern day horses, which are better suited for grasslands as they can escape predators easily and travel great distances to search for food
  • Transitional fossils: share traits of modern descendants & prehistoric ancestor→ illustrate an evolutionary transition
    > Tiktaalik: similar to fish ancestors as it had gills and scales, and to tetrapod descendants as it had tetrapod leg bones, lungs, upward positioned eyes→ shows fish are the ancestors to modern tetrapods
    > Archaeopteryx: teeth, bony tail of a reptile & feathers like bird→ intermediate between birds and dinosaurs
41
Q

What is biogeography?

A

study of past and present patterns of geographical distribution of organisms–> supports common ancestry

42
Q

Explain how biogeography support Darwin’s theory of evolution by NS

A
  • Biogeographic realms→ closely related species and their common ancestors present in the same geographical region
    > Species originate in one area and spread outwards
    OR
  • Modification shaped by NS due to differences in the local env
  • From common ancestor on supercontinent–> continental drift–> populations isolated on diff continents–> gene flow disrupted, diff selection pressures
  • Mesosaurs’ fossils are distributed across Africa and South America, which are separated by Atlantic ocean. Ancestral species of mesosour, on a supercontinent joining these 2 continent, gave rise to variety of mesosaur species that radiated out in this ancient supercontinent. When continents broke up and separated, fossilised remains transported to where they are today.
  • Lungfish’s fossils found worldwide: Common ancestor dispersed from centre of origin when continents were still merged. Continental drift→ ancestors geographically separated
  • Biogeographic distribution of finches supports descent w modification as finches came from ancestral species from mainland, which then evolved into diff species through adaptive radiation
43
Q

How do genetic variations arise?

A
  • Gene mutations: substitution, deletion, insertion→ change triplet code→ change aa seq
  • Chromosomal mutations: numbe, structure
  • Meiosis: independent assortment and crossing over
  • Sexual reproduction: random fusion of gametes
44
Q

How does heterozygote protection/diploidy preserve genetic variation?

A

Expression of dominant alleles mask the expression of recessive alleles→ disadvantageous trait doesn’t manifest→ not selected against→ even if recessive alleles less favourable/harmful, they persist and are propagated in heterozygotes

45
Q

Explain how balancing selection helps to preserve genetic variation

A
  • Balancing selection: NS maintains 2 or more allele at a locus
  • Heterozygote advantage: heterozygotes have greater fitness than both kinds of homozygotes
    > Heterozygotes with HbAHbS genotype don’t develop sickle-cell anaemia and have less chance of contracting malaria→ sickle cell trait is selected for in malaria-infected regions→ survive and reproduce→ both alleles remain in population
  • Frequency-dependent selection: population maintains stable freq of 2 phenotypic forms→ alleles coding for them preserved
    > Scale-eating fish in Lake Taganyika are either “left-mouthed”, which attacks prey’s right side, or “right-mouthed”, which attacks prey’s left side. Prey guards itself against attack from whatever phenotype of scale-eating fish is most common in the lake
    From year to year, selection favours whichever mouth phenotype is less common→ freq of left and right-mouthed fish oscillates over time & is kept close to 50%

Alevel Biology (16 decks)

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