SELECTION PRESSURE

Question 1

Natural Selection

Answer 1

process in which those organisms whose alleles give them a selective advantage are more likely to survive, reproduce and pass on their alleles to the next generation (Intraspecific competition is important for it)

Question 2

Stabilising Selection

Answer 2

few organisms survive at extremes which means that is selects for the mean which remains unchanged, it occurs in non-changing environment and is repeated over many generations
e.g. Very big animal is too slow but very small animal is too weak, therefore middle pathway is best

Question 3

Directional Selection

Answer 3

Organisms with a particular extreme of phenotype have a selective advantage
e.g. Bacteria which gain resistance

Question 4

Disruptive Selection

Answer 4

Selection against middle, selection for one extreme
e.g. Bird species called ‘finches’, smaller beaks helped catching insect, larger beaks helped opening seed, middle sized beaks were useless

Question 5

Process of Speciation

Answer 5

Isolation between two populations (if the isolation has been due to separation of lands, then write GEOGRAPHICAL ISOLATION between two populations)
No gene flow i.e. interbreeding between populations
Variation
There are different environmental factors which allow a certain characteristic to survive
Mutation
Some organisms have allele to adapt and therefore survive , for example mutation allele may produce camouflage
Adaptive organisms survive and reproduce
There is an increase in the frequency of the surviving allele
Gene pool differs from original species, therefore no interbreeding can occur
This occurs over a long period of time

Question 6

Reproductive Isolation

Answer 6

Organisms cannot breed with another group

Question 7

When a species is isolated

Answer 7

1) Less competition

2) Less predators

Question 8

Speciation is a lot less frequent these days

Answer 8

Similar biotic and Abiotic pressures
Similar selection pressures
No isolation