Natural Selection

Question 1

Explain the Median Grown Finch Example:

Question 2

Explain the Rock Pocket Mice Example:

Question 3

What is positive directional selection?

Answer 3

Favours individuals on one end of the distribution of phenotypes. (Graph skewed left or right).

Question 4

What is stabilising directional selection?

Answer 4

Favors those in the middle.

Question 5

What is disruptive directional selection?

Answer 5

Favours those at either end (the extreme).

Question 6

What is industrial melanism, and why is it important?

Answer 6

• directional selection
• incomplete dominance
• selection acts on dominant alleles faster than recessive
• favoured dominant alleles immediately increase in frequency.
• selection is not likely to drive a dominant allele to fixation as recessive alleles can hide in a heterozygous state.
• favoured recessive alleles are not exposed to selection initially bc they are likely to occur only in heterozygous genotypes.
• only recessive hemozygous begin to appear they quickly fix in the population

Question 7

What are examples of stabilising selection?

Answer 7

1. Birth clutch size
2. birth weight of human babies
3. number of fingers
4. camouflage to match environment

Question 8

What are examples of disruptive selection?

Answer 8

1. Specialist seeding
2. smal fish eat algea
3. big fish eat small insects

Question 9

What are examples of artisicial selection?

Answer 9

1. humans chosen for traits
2. agriculture
3. dog breeding

Question 10

What are examples of balancing selection?

Answer 10

• heterozygote advantage occurs when selection savours heterozygous individuals over homozygotes
• heterozygotic for sickle cell anaemia for protection against malaria.

Question 11

Explain the role of fitness in Natural selection.

Answer 11

Fitness = success of an organism at surviving and reproducing and thus contributing offspring to future generations.

Question 12

Explain the role of relative fitness in natural selection:

Answer 12

• (w) = describes the success of a genotype at producing new individuals.
• Relative fitness standardised by the success of other genotypes in the population ranges from 0-0.10.
• Able to:
  1. calc exp frequencies using HWE.
  2. Ratio of observed/expected
  3. Relative fitness: AS>AA>SS