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Flashcards in 8.3 Deck (24):
1

Species:

a group of similar organisms that can interbreed to produce fertile offspring

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Speciation:

the evolution of a new species

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New species may arise in 2 different ways:

Allopatric speciation
Sympatric speciation

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Individuals from 2 different species cross-fertilise and produce a...

fertile hybrid

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Groups within the population become isolated from one another and cannot interbreed, this is called...

reproductive isolation

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Reproductive isolation, gene flow amongst the separate groups is prevented and the population's single gene pool is now...

split into several separate gene pools

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Reproductive isolation, allele frequencies within each gene pool may change because....

selection pressures acting on the phenotypes of the organisms may be different

8

Reproductive isolation, the gene pools may become so different from each other that...

successful interbreeding is no longer possible and each group is now a different species within its own gene pool

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Allopatric speciation occurs when:

populations are prevented from interbreeding because they become geographically isolated

10

Allopatric speciation, the selection pressures in the 2 areas result in the gene pools of the 2 groups becoming very different there is no...

gene flow between the 2 groups

11

Sympatric speciation occurs when...

populations living together become reproductively isolated

12

Sympatric speciation may take place :

before mating occurs - preventing the exchange of gametes (prezygotic mechanisms)

after mating - preventing the development of the zygotes into offspring (postzygotic mechanisms)

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5 prezygotic variations:

geographical
ecological
temporal
behavioural
mechanical

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1 post-mating but prezygotic variation:

gametic

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3 postzygotic variations:

hybrid sterility
hybrid inviability
hybrid breakdown

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what is geographical variation:

populations are isolated by physical barriers (oceans, mountains, rivers)

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what is ecological variation:

populations inhabit different habitats within the same area and so individuals rarely meet

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what is temporal variation:

the breeding seasons of each population do not coincide and so they do not interbreed

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what is behavioural variation:

mating is often preceded by courtship, which is stimulated by the colour or markings of the opposite sex, the call or particular actions of a mate. Any variations in these patterns may prevent mating.

20

What is mechanical variation?

Anatomical differences may prevent mating occurring

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What is gametic variation?

The gametes may be prevented from meeting due to genetic or biochemical incompatibility

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What is hybrid sterility?

Hybrids formed from the fusion of gametes from different species are often sterile because they cannot produce gametes

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What is hybrid inviability?

despite fertilisation taking place, further development does not occur or fatal abnormalities arise in early growth

As the offspring do not reach sexual maturity, breeding does not occur

24

What is hybrid breakdown?

The first generation of hybrids is fertile but the second generation fails to develop or, if it does, it is sterile