4.4 Gentic Diversity

Question 1

1. What is meant by ‘genetic diversity’?

Answer 1

The number of different alleles of genes in a population

Question 2

2. Describe the process of natural selection:

Answer 2

• Random mutations create new alleles of genes
• Therefore there is variation between individuals in the population
• Some mutations are harmful…
• BUT in certain environments the new allele means the individuals with it have a selective advantage
• So they survive and reproduce
• And pass on their advantageous alleles
• to the next generation
• So the frequency of that allele increases in the population

Remember: Malt Vinegar And Salt Really Are Good Flavours
OR: Many Very Angry Silly Red Arctic Goats Fart

Question 3

3. What is directional selection?

What happens to the mean characteristics of the population and the standard deviation?

Answer 3

Selection that may vary in one direction from the mean of the population.
Extreme phenotypes have a selective advantage and this results in the characteristics of the population changing over time.
(the mean characteristic of the population changes, but the standard deviation stays the same)

Question 4

4. Add a line to each graph to show how the two ways that directional selection could change the population:
   EITHER:

Answer 4

0

Question 5

5. Describe how antibiotic resistance in bacteria spreads throughout a bacterial population.
   Why is this an example of directional selection?

Answer 5

• There is variation in the original population of bacteria (due to previous random mutations)
• This means that some bacteria are more resistant to antibiotics than others
• When antibiotics are applied to the population the least resistant bacteria die and the most resistant ones survive
• Therefore, the most resistant bacteria reproduce and pass on their advantageous alleles (which make them resistant to antibiotics) to their offspring
• So the frequency of alleles which give resistance to antibiotics increases in the population
This is an example of directional selection because an extreme phenotype has a selective advantage (i.e. the most resistant bacteria have an advantage over the least resistant bacteria). So over time the number of less resistant bacteria will decrease and the number of more resistant bacteria increases.

Question 6

6. What is stabilising selection? What happens to the mean characteristics of the population and the standard deviation?

Answer 6

Selection that favours average individuals. This preserves the characteristics of a population

Question 7

7. Add a line to the graph to show how stabilising selection would change the population.

Answer 7

0

Question 8

8. Describe how baby birth weight is affected by natural selection
   Why is this an example of stabilising selection?

Answer 8

• There is variation in the size of babies at birth
• The smallest and the biggest babies have the lowest chance of survival
• This means that the ‘medium’ weight babies are most likely to survive and reproduce and pass on their alleles (which make them this intermediate weight) to their offspring
• So the frequency of alleles which give intermediate weight increase in the population
This is an example of stabilizing selection because the extreme phenotypes are selected against (i.e. the biggest and smallest babies are least likely to survive). And instead the ‘average’ phenotype has a selective advantage (i.e. intermediate weight babies are more likely to survive and reproduce). So over time the number of really big and really small babies decreases and the number of intermediate weight babies increases.

Question 9

9. Give three reasons it is important to us aseptic techniques when working with microbes

Answer 9

• To prevent contamination of apparatus with other microorganisms/bacteria
• To prevent personal contact with bacteria
• To prevent release of bacteria into air

Question 10

10. Explain the purpose of each of these steps of aseptic technique
    • Wiping surfaces with ethanol

Answer 10

To kill any microbes on the surface

Question 11

• Working underneath a lit Bunsen burner

Answer 11

To create up up-flow of air, so no microbes or dust fall onto your experiment

Question 12

• Flaming the necks of bottles containing microbial cultures

Answer 12

Passing the mouth of the bottle through a flame produces a convection current away from the opening, and helps to prevent contamination
This ensures that no microorganisms enter the mouth of the vessel to contaminate the culture or the medium.