evolution

Question 1

evolution

Answer 1

change in the genetic composition of a population during successive generations, which may result in the development of new species

Question 2

microevolution

Answer 2

small-scale allele frequency variation within a species, where the descendant is in the same taxonomic group to the ancestor

e.g. antibiotic-resistance bacteria

Question 3

macroevolution

Answer 3

allele frequency variation at or above species level over time, resulting in the divergence of taxonomic groups, where the descendant is in a different taxonomic group to the ancestor

e.g. African cichlids

Question 4

evolutionary radiation

Answer 4

increase in taxonomic diversity through speciation

(rapid or slow)

Question 5

mass extinction

Answer 5

loss of ≥75% of all species

(rapid)

Question 6

natural selection

Answer 6

variation between offspring; heritable traits; more offspring produced than can survive

individuals best suited to the environmental selection pressures have greater viability (survivability) & fecundity (fertility)

Question 7

allele frequency expression

Answer 7

[2(# of homozygotes) + (# of heterzygotes)] ÷ 2(# of individuals)

Question 8

positive & negative selection pressures of allele frequency

Answer 8

positive : favours a particular allele; increasing its frequency

negative : opposes a particular allele; decreasing its frequency

Question 9

gene flow

Answer 9

exchange of alleles between populations from migrating individuals who then reproduce

new alleles change the genetic composition (gene pool) of the population

Question 10

genetic drift

Answer 10

change in allele frequency of a population over time due to random events

greater impact on small, isolated populations

e.g. bottleneck & founder effect

Question 11

bottleneck effect

Answer 11

random natural or anthropogenic event reduces the population size & gene pool

∴ ↓allele frequency & ↓genetic diversity

Question 12

why are small populations with reduced genetic diversity (i.e. those affected by the bottleneck effect) more susceptible to genetic drift & face an increased risk of extinction ?

Answer 12

low genetic diversity → decreased fitness (viability & fecundity)

low genetic diversity → decreased genetic ability to evolve

small gene pool & low gene flow cannot buffer against these chance events

(less resilient & less adaptable)

Question 13

founder effect

Answer 13

small group of individuals from a population separate & colonize new territory

∴ ↓allele frequency & ↓genetic diversity

(new, small & less diverse population)

Question 14

stabilizing selection

Answer 14

intermediate phenotype is favoured & extreme phenotypes are selected against

occurs from stable environments

Question 15

directional selection

Answer 15

one extreme phenotype is favoured & other extreme phenotype is selected against

population distribution shifts towards the former

occurs from gradual or sustained changes in environmental conditions

Question 16

disruptive selection

Answer 16

both extreme phenotypes are favoured & intermediate phenotype is selected against

occurs from fluctuating environmental conditions (e.g. seasonal changes)

bimodal spread may lead to reproductive isolation & speciation

Question 17

divergent evolution

Answer 17

two species evolve from a common ancestor

homologous structures (derived from a common ancestor; evolved to have different functions)

∵ different selective environmental pressures

e.g. Darwin’s finches

Question 18

convergent evolution

Answer 18

two unrelated species independently evolve to become similar

analogous structures (evolved to have similar functions; derived from unrelated ancestors)

∵ similar selective environmental pressures

e.g. sharks & dolphins

Question 19

parallel evolution

Answer 19

two species with a common ancestor independently evolve to become similar

∵ similar selective environmental pressures post separation

e.g. polydactyly chickens

Question 20

co-evolution

Answer 20

two species evolve by exerting selection pressures on each other

e.g. lions & zebras

Question 21

speciation

(macroevolutionary changes)

Answer 21

accumulation of microevolutionary changes over time

∵ mutation, gene flow, genetic drift

Question 22

allopatric speciation

Answer 22

reproductive isolation (no gene flow) caused by geographical isolation (physical barrier)

Question 23

sympatric speciation

Answer 23

reproductive isolation (non-random mating) caused by temporal, mechanical or behavioral isolation (genetic polymorphism)

(continuous but reduced gene flow)

Question 24

parapatric speciation

Answer 24

reproductive isolation (non-random mating) caused by ecological isolation (separate niches)

(continuous but reduced gene flow)

Question 25

reproductive isolation

Answer 25

barriers that prevent gene flow (interbreeding) between individuals leading to speciation