10.3 (bioninja summary)

Question 1

what is evolution (gene pools)

Answer 1

Evolution is the change in the allele frequency within a gene pool
over several successive generations

Question 2

what is a gene pool

Answer 2

the sum total of all the genes (and the alleles)
that are present within an interbreeding population

Question 3

what is allele frequency

Answer 3

the relative proportion of a
particular allele within a population

Question 4

effect of genetic drift on gene pools

Answer 4

changes the composition of a gene pool due to random / chance events within the population
* There is higher drift in smaller populations (faster change)
* There is lower drift in larger populations (greater stability)

Question 5

effect of natural selection on gene pools

Answer 5

changes the composition of a gene pool due to environmental selection pressures
* Selection may be stabilising, directional or disruptive

Question 6

population bottlenecks

Answer 6

• occur when an event reduces the
  population size by an order of magnitude
• Surviving population has less genetic variability (⇧ drift)

Question 7

founder effect

Answer 7

• establishment of a new
  population by a fraction of a larger existing population
• new population has less genetic variability (⇧ drift)

Question 8

3 types of selection

Answer 8

imagine these as graphs
- stabilising selection (culls extremes)
- directional selection (favours one extreme)
- disruptive selection (favours both extremes)

Question 9

what is stabilising selection +example

Answer 9

When an intermediate phenotype is
favored at the expense of extremes
* Operates when conditions are STABNLE
* Example: Human birth weights
⇨ Too large = birth complications
⇨ Too small = high infant mortality

Question 10

what is directional selection +example

Answer 10

When one phenotypic extreme is
selected at the cost of the other
* Operates when conditions CHANGE
* Example: Antibiotic resistance
⇨ Antibiotic = ⇧ resistance
⇨ No antibiotic = ⇧ susceptibility

Question 11

what is disruptive selection + example

Answer 11

When both extremes are favored at
the expense of the intermediate
* Operates when conditions FLUCTUATE
* Example: Moth pigmentation
⇨ Pigmentation = camouflage
⇨ Benefit depends on conditions

Question 12

when does reproductive isolation occur

Answer 12

when barriers prevent two
populations from interbreeding (gene pools kept separate)

= gradual accumulation of genetic diffs = speciation

Question 13

2 types of repro isolation barriers

Answer 13

• Pre-zygotic barriers (no offspring are produced)
• Post-zygotic barriers (offspring are not viable or infertile)

Question 14

3 types of pre-zygotic barriers

Answer 14

temporal – populations have repro cycles at diff times (distinct from e/o)

behavioural – populations exhibit/respond to specific courtships

geographic isolation – occupy diff habitats / niches in an area

Question 15

allopatric speciation

Answer 15

Occurs when geographic barriers isolate populations
*physically separated populations are exposed to different environmental conditions and begin to diverge

Question 16

sympatric speciation

Answer 16

Occurs when populations diverge within a shared location
* Reproductive isolation leads to genetic divergence

Question 17

sympatric speciation – polyploidy

Answer 17

a possible cause
A failure to undergo cytokinesis during meiosis results in
gametes with additional sets of chromosomes (not haploid)
- more common in self pollinating / axesual plants

Question 18

2 models for speciation pace

Answer 18

• phyletic gradualism (gradual)
• punctuated equilibrium (rapid bursts)

Question 19

Phyletic Gradualism

Answer 19

Speciation occurs at a constant pace over a period of time
* Involves a continuous / gradual accumulation of mutations
* Theory is supported by the presence of intermediate
fossils (e.g. evolution of the modern horse hoof)

Question 20

Punctuated Equilibrium

Answer 20

• Speciation occurs in rapid bursts with periods of stability
• If conditions are stable, characteristics are maintained
• Environmental change promotes rapid divergence
• Gaps in the fossil record provide support for this theory