Topic 8.3 Gene pools

Question 1

Define population

Answer 1

All the organisms of a particular species that live in the same place

Question 2

Give examples of selection preasures

Answer 2

• Predatation
• Disease
• Competition (for food, habitats, mates)
• Enviromental conditions e.g. temperature

Question 3

How do selection preasures change alleles frequencies within a polulation?

Answer 3

Organisms with advantageous charecteristics are more likely to be survive and produce offspring. Therefore their favourable alleles get passed on, while unfavourable alleles die out.

Question 4

What is directional selection?

Answer 4

Directional selection moves the mean value for a charecteristic in one direction, changing the whole population

Question 5

What is stabilising selection?

Answer 5

Occurs when enviromental conditions stay the same. Individuals closest to the mean are favoured, and any new charecteristics are selected against. Results in low diversity.

Question 6

What is disruptive selection?

Answer 6

The opposite of stablising selection, in that both extremes of the normal distribution are favoured over the mean. Over time, the population becomes phenotypically divided and new species may develop.

Question 7

Define genetic drift

Answer 7

A change in the population’s allele frequencies that occurs due to chance rather than selective preasures. In other words, it is caused by ‘sampling error’ during reproduction.

Question 8

What is meant by a population bottleneck?

Answer 8

Where a catastrophic event dramatically reduces the size of a population, thereby decreasing the variety of alleles in the gene pool and causing large changes in allele frequencies.

Question 9

What is meant by the founder effect?

Answer 9

When a small number of individuals become isolated, forming a new polulation with a limited gene pool, with allele frequencies not reflective of the original population.

Question 10

What is the Hardy-Weinberg principle?

Answer 10

Allows us to estimate the frequency of alleles in a population, as well as if allele frequency is changeing over time.

Question 11

Give the assumptions made by the Hardy-Weinburg principle

Answer 11

• No mutations occur to create new alleles
• No migration in or out of the population
• No selection, so alleles are equally passed onto the next generation
• Random mating
• Large population

Question 12

Explain the Hardy-Weinburg equation for calculating allele frequency

Answer 12

The frequencies of each allele for a charecteristic must add up to 1.0. The equation is therefore; p+q=1

Where p = frequency of the dominant allele, and q = frequency of the recessive allele.

Question 13

Explain the Hardy-Weinburg equation for calculating genotype frequency

Answer 13

The frequencies of each genotype for a charecteristic must add up to 1.0. The equation is therefore; p² + 2pq + q² = 1

Where p² = frequency of homozygous dominant, 2pq = frequency of heterozygous, and q² = frequency of homozygous recessive.