8.3

Question 1

Species:

Answer 1

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

Question 2

Speciation:

Answer 2

the evolution of a new species

Question 3

New species may arise in 2 different ways:

Answer 3

Allopatric speciation

Sympatric speciation

Question 4

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

Answer 4

fertile hybrid

Question 5

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

Answer 5

reproductive isolation

Question 6

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

Answer 6

split into several separate gene pools

Question 7

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

Answer 7

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

Question 8

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

Answer 8

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

Question 9

Allopatric speciation occurs when:

Answer 9

populations are prevented from interbreeding because they become geographically isolated

Question 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…

Answer 10

gene flow between the 2 groups

Question 11

Sympatric speciation occurs when…

Answer 11

populations living together become reproductively isolated

Question 12

Sympatric speciation may take place :

Answer 12

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

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

Question 13

5 prezygotic variations:

Answer 13

geographical
ecological
temporal
behavioural
mechanical

Question 14

1 post-mating but prezygotic variation:

Answer 14

gametic

Question 15

3 postzygotic variations:

Answer 15

hybrid sterility
hybrid inviability
hybrid breakdown

Question 16

what is geographical variation:

Answer 16

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

Question 17

what is ecological variation:

Answer 17

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

Question 18

what is temporal variation:

Answer 18

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

Question 19

what is behavioural variation:

Answer 19

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.

Question 20

What is mechanical variation?

Answer 20

Anatomical differences may prevent mating occurring

Question 21

What is gametic variation?

Answer 21

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

Question 22

What is hybrid sterility?

Answer 22

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

Question 23

What is hybrid inviability?

Answer 23

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

Question 24

What is hybrid breakdown?

Answer 24

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