[18.3-4] natural selection, effects of selection on evolution

Question 1

describe the core of natural selection (5)

Answer 1

1. genetic diversity in a population due to random mutations (gene pool)
2. ability to reproduce and pass on alleles (genes)
3. selective pressures in the environment leads to differential survival
4. those that have a selective advantage will be more likely to survive and reproduce, thus passing on advantageous alleles
5. over many generations desired alleles will increase in frequency

Question 2

what are selection pressures?

Answer 2

environmental factors that limit the population of a species

Question 3

what are some examples of selection pressures? (3)

Answer 3

• predation
• disease
• competition

Question 4

what factors does the process of evolution by natural selection depend on?

Answer 4

• organisms produce more offspring than can be supported by the available supply of food, light, space etc.
• genetic variety within the populations of all species
• variety of phenotypes that selection operates against

Question 5

what are the 3 types of natural selection?

Answer 5

• stabilising
• directional
• disruptive

Question 6

draw the graph!

describe stabilising selection

Answer 6

• favours average phenotype (phenotype around the mean)
• selection against extreme phenotypes
• tends to occur where the environmental conditions are constant over long periods of time

Question 7

draw the graph!

describe directional selection

Answer 7

• changes phenotype of a popuation
• favours phenotypes that vary in one direction from the mean in the population ie. extreme phenotype
• due to change in environmental condition

Question 8

draw the graph!

describe disruptive selection

Answer 8

• favours individuals with extreme phenotypes rather than those with phenotypes around the mean of the population
• occurs when an environmental factor takes two or more distinct forms