Evolution, Natural selection and speciation

Question 1

Directional selection

Answer 1

this is where the environmental conditions change so one extreme of phenotype is favoured. the individuals with this extreme phenotype are more likely to survive and pass on their alleles.

Question 2

stabilising selection

Answer 2

usually occurs when the environmental conditions stay stable for quite sometime. extreme phenotypes are selected against so are less likely to pass their alleles onto the next generation. selection favours average individuals.

Question 3

species

Answer 3

organism that can breed together to produce fertile offspring

Question 4

allopatric speciation

Answer 4

one population gets split into 2 due to geographical isolation e.g. a river

Question 5

sympatric speciation

Answer 5

occurs when populations of an original species living in the same area /environment become reproductively isolated.

Question 6

reproductive isolation may occur as a result of:

Answer 6

seasonal changes/temporal isolation: two or more. species live in the same area but are reproductively active at different times and cannot breed together
behavioural changes: where two different populations evolve courtship displays not recognised by the other. this prevents them from being attracted to and breeding with the other.
mechanical changes/gametic variation: 2 populations are unable to interbreed due to e.g. differences in genetalia