7. Natural selection

Question 1

define discontinuous variation

Answer 1

distinct forms with no intermediate types

Question 2

define continuous variation

Answer 2

no distinct categories, most likely to form a bell shaped curve

Question 3

name the two causes of variation

Answer 3

1. environmental i.e. water availability, light intensity
2. genetic i.e. mutations, meiosis

Question 4

name the different types of natural selection

Answer 4

1. stabilising
2. directional
3. disruptive

Question 5

define stabilising selection

Answer 5

• organisms are more likely to survive with characteristics in the middle of the range
• when the environment is constant

Question 6

define directional selection

Answer 6

• individuals with alleles with extreme phenotypes are more likely to survive
• this is due to their changing environment

Question 7

define disruptive selection

Answer 7

• individuals with alleles for extreme phenotypes either way are more likely to reproduce
• as their environment constantly changes
• meaning these organisms need to have many characteristics