Topic 7B: Evolution

Question 1

Define the biological term species. [1]

Answer 1

1. A group of organisms that can interbreed to produce fertile offspring

Question 2

Define the biological term population. [2]

Answer 2

1. A group (of organisms) of the same species in a (particular) space at a (particular) time;
2. That can (potentially) interbreed

Question 3

Why is antibiotic resistance in bacteria an example of directional selection? [4]

Answer 3

1. BY random mutations, some bacteria have allele for resistance;
2. Use of antibiotics is the selection pressure: non-resistant bacteria die;
3. Resistant bacteria more likely to survive to reproduce and pass on their alleles;
4. Frequency of the resistant allele increases in the bacterial population;
5. Frequency of antibiotic resistance increases in the bacterial population

Question 4

The ability for humans to continue producing lactase is known as lactase persistence (LP) and is controlled by a dominant allele. One hypothesis for LP in humans suggests that the selective pressure was related to some human populations farming cattle as a source of milk.

Describe how this could have led to an increase in LP. [4]

Answer 4

1. LP due to mutation
   OR
   Allele due to mutation;
2. Milk provides glucose/galactose/protein;
3. Individuals with LP/advantageous allele more likely to survive and reproduce;
4. Directional selection;
5. Frequency of allele increases (in the offspring/next generation)

Question 5

The ability for humans to continue producing lactase is known as lactase persistence (LP) and is controlled by a dominant allele.

Explain why the number of people showing LP would rapidly increase once selection for this condition has been established. [2]

Answer 5

1. Dominant allele;
2. (Always) expresses
   OR
   Expressed when only one (dominant allele) present

Question 6

Climate change has reduced the survival rate of snowshoe hares in mountain habitats.

Suggest and explain how. [2]

Answer 6

1. Less snow so less camouflage;
2. More hares seen/eaten/killed by predators

Question 7

In the mountains, when winter changes into spring, the coat colour of snowshoe hares changes from white to brown. Climate changes have caused the snow to melt earlier. This reduced the survival rate of snowshoe hares in these habitats. The change in coat colour occurs when new fur replaces old fur. This is called moulting.

Snowshoe hares within a population mault at different times.

Explain how this could ensure the survival of snowshoe hare populations in these mountain habitats. [4]

Answer 7

1. Hares which mault earlier (more likely to) survive;
2. Hares which mault earlier (more likely to) reproduce;
3. Pass on (advantageous) allele;
4. Frequency of allele increases (in future populations)

Question 8

A recessive allele which has harmful effects is able to reach a higher frequency in a population than a harmful dominant allele. Explain how. [3]

Answer 8

1. Recessive alleles can be carried by individuals without showing effects
   OR
   Dominant allele always expressed;
2. Organism that carries more likely to reproduce
   OR
   Affected organism less likely to reproduce;
3. (Therefore) recessive alleles are more likely to be passed on
   OR
   Dominant alleles less likely to be passed on

Question 9

What is a gene pool? [1]

Answer 9

1. All the alleles in a population

Question 10

Lord Howe island in the Tasman Sea possesses two species of palm tree which have arisen via sympatric speciation. The flowering times of the two species are different.

Using this information, suggest how these two species of palm tree arose by sympatric speciation. [5]

Answer 10

1. Occurs in the same habitat/environment/population;
2. Mutation(s) causes different flowering times;
3. Reproductive separation/isolation
   OR
   No gene flow
   OR
   Gene pools remain separate;
4. Different allele(s) passed on/selected
   OR
   Change in frequency of allele(s);
5. **Disruptive (natural) selection;
6. Eventually different species cannot (inter)breed to produce fertile offspring