Population and Evolution (Chapter 18)

Question 1

Describe the stages of natural selection

Answer 1

1) Mutation takes place.
2) Some are better adapted to survive so they are more likely to reproduce and pass on alleles.
3) Over time the frequency of advantageous alleles increases in the population.

Question 2

Define Disruptive Selection

Answer 2

Favours individual at both extremes of the mean and those nearer the mean are selected against.

Question 3

Define Species

Answer 3

A group of individuals with similar genes that are able to breed together to produce fertile offspring.

Question 4

Define Gene Pool

Answer 4

All the alleles in a population

Question 5

Describe Directional Selection

Answer 5

When there is environmental change so there is selective pressure for a species to change in response to it.

Favours individuals at one extreme of the range. Individuals selected against at other side of the mean and the mean shifts.

Question 6

Describe Stabilising Selection

Answer 6

When there is no environmental change and it remains stable. Individuals with phenotypes closest to the mean are favoured for. Individuals with extreme phenotypes are selected against, reducing them, so distribution curve becomes narrower.

Question 7

Define Speciation

Answer 7

Evolution of a new species from an existing one.

Question 8

Define Geographical Isolation and its two types

Answer 8

When 2 populations become isolated by a barrier forming called allopatric speciation. Or within a population called sympatric speciation where they become reproductively separated within the same area.

Question 9

Describe the Process of Speciation by Geographical Isolation

Answer 9

1) Two gene pools cannot mix
2) Populations face different selection pressures as they have different environmental conditions
3) Selection for specific alleles over a long period of time
4) Allelic frequency changes
5) Eventually become so different that they are unable to interbreed so become different species