Speciation

Question 1

biological definition of species

Answer 1

population of reproducing organisms that is isolated (cant exchange genes) from other populations

Question 2

what problems apply to the biological definition of species

Answer 2

prokaryotes and eukaryotes that arent strictly sexual, doesnt apply to them

impossible to use with extinct organisms
and also bacteria/archaea w/ horizontal gene transfer

Question 3

what situations can species appear

Answer 3

• in TIME along a lineage splitting off during evolutions
• in SPACE due to geographical isoltion
• GENETIC EFFECTS could be even a single bp change
  can be identified using pop. gneetics)

Question 4

allopatric speciation

Answer 4

classic form of speciation
pop geopgraphically isolated from each other –> reproductive islation (no gene floe)

doesn’t have to be diff selection pressures but can be

Question 5

types of selection effects

Answer 5

directional selection - one extreme version of a population survives

disruptive selection - only extreme forms survive

stabilizing selelction - extreme forms disappear

see one note for example

Question 6

Genetic drift

Answer 6

no selection pressure
prurely randome effects

more likely in small populations - theyre more at risk

Question 7

Founder effect/bottleneck

Answer 7

an event causes a reduction in a pop’s size and gene pool

founder effect:
new pop established by small number of indivudals

e.g. a bird gets blown away to some islands,
an entire type of allele can be left behind cuz the bird doesnt have it

Question 8

sympatric speciation and its potential causes

Answer 8

populations that aren’t geograhpically isolated, but reproductively isolated

minimal evidence for animals doing this

but plants more likely

Question 9

assortative mating + an exmaple

Answer 9

selection where individuals with similar pheno/genotypes interbreed more frequently than ocmplete random mating

e.g. Blackcap birds - spanish birds breed with each other, UK birds with each other

probs due to arrival time on breeding grounds

but it saw reproductive isolation between 2 groups

Question 10

polyploid speciation

Answer 10

happens in plants only

cells of an organism have more than one pair of homologous chromosomes

its a failure of cell division,
basically it forms diploid gametes (so DNA doubles in offspring instead of being identical)

therefore the next generation are genetically isolated from the normal population

see one note for diagram

Question 11

Barriers in mating - prezygoting barriers

Answer 11

blocks reproduction by preventing fertilisation

caused by:
(pre mating)
habitat isolation
temporal isolation
behavioural isolation
(post mating)
mechanical isolation
gametic isolation

so no mating can take place, or if it does - not compatible

Question 12

Barriers in mating - postzygotic barriers

Answer 12

blocks reproduction after fertilization

causes:

reduced hybrid viability (doesnt survive)
reduced hybrid fertility (can’t reproduce)
hybrid breakdown (can reproduce once but not again)

Question 13

Hybrid zones

Answer 13

after speciation occurs, it’s the possible outcomes if the two species interbreed and make hybrids (very likely if they’re still in the same habitat)

possible outcomes:

Reinforcement - remains as 2 distinct species, hybrids are less fit so they eventually die out, the species contirnue to diverge until hybridisation cant occur

Fusion - reproductive barriers weaken, the two species eventually become one again

Stability - Two species remain distinct, fit hybrids continue to reproduce, everyone lives happily ever after

see one note for diagrams

Question 14

In what situation would natural selection act to reinforce reproductive isolation?

Answer 14

When 2 pops are diverged enough to produce hybrids
But the hybrids are unfit
nat selec will act to prevent the formation of these unfit hybrids
By strenthening reproducitve isolations
via REINFORCEMENT