Paper 2 - Genetic Diversity And Adaptation

Question 1

What is evolution ?

Answer 1

A change in the allele frequencies and inherited characteristics of a population over time through the process of natural selection which may lead to a formation of a new species.

Question 2

The process of natural selection

Answer 2

• Variation occurs due to a mutation.
• Different selection pressures (predation/competition/disease/environmental factors)
• There’s a selective advantage of the new allele to the organism
• Individuals with the advantageous allele are more likely to survive, reproduce and pass on the the advantageous allele to their offspring.
• The frequency of this advantageous allele increases over time.

Question 3

Describe how natural selection can lead to antibiotic resistance.

Answer 3

1. Some bacteria have a mutation containing the allele fro antibiotic resistance.
2. Person infected with bacteria takes antibiotic which kills all suspecitble bacteria.
3. Person stops taking antibiotic. The bacteria with the alle for resistance has survived.
4. Resistant bacteria can now divide/reproduce by binary fission, passing on the allele.
5. Frequency of resistant allele increases in population
6. Bacteria is now resistant to that antibiotic.

Question 4

Stabilising selection

Answer 4

• Acts against both extremes in a range of phenotypes
• The mode stays the same, but the range of phenotypes decreases
• Example: human birth weight has become stabilised around the optimum size for maximum survival.

Question 5

Directional selection

Answer 5

• Acts against one of the extremes in a range of phenotypes
• One phenotype becomes rare and an alternative becomes kore common
• This increases the frequency of one phenotype relative to another
• This occurs when there are 2 different allies for a gene, and so, one is more beneficial than the other
• Example: bacterial antibiotic resistance

Question 6

Disruptive selection

Answer 6

• Individuals with both extremes of a phenotype have a selective advantage over those in the midddle
• Links to evolution and change and speciation (development of new species)
• Example: Pacific Coho salmon where large males and small males have a selective advantage over middle-sized males in passing on their alleles.

Question 7

Adaptations

Answer 7

Anatomical e.g. fur colour in mice
Physiological e.g. having Hb with a different oxygen affinity
Behavioural e.g. tool use in chimps

Question 8

Causes of Reduced Genetic Diversity - Genetic Bottleneck

Answer 8

A population is temporarily rescued to every small number when most individuals are killed - could be done by flooding, volcanic eruptions, etc. This may result in a dramatic reduction in genetic diversity/ smaller gene pool

Question 9

Causes of Reduced Genetic Diversity - Founder Effect

Answer 9

A few organisms from a population become isolated from the rest. For example, when a small no of individuals emigrate from the parent population and colonise a new region such as an island. These individuals will carry a small fraction of the alleles present = reduction in genetic diversity/ gene pool.

Question 10

Causes of Reduced Genetic Diversity - Inbreeding

Answer 10

If the organisms are only able to breed with a limited number of individuals then this can reduce genetic diversity further and sometimes amplify genetic disorders.