Genetic Diversity & Adaptation

Question 1

Define natural selection

Answer 1

The process by which organisms that are better adapted to their environment survive and reproduce in greater numbers, resulting in the increase of the frequency of the advantageous allele within the population.

Question 2

What are the different types of adaptations?

Answer 2

• Anatomical (related to anatomy)
• Physiological (related to normal function of body systems)
• Behavioural (the organisms behaviour in the environment)

Question 3

What are the stages of natural selection?

Answer 3

1. Selection presuures within the environment may change
2. Variation caused by mutation leads to new alleles of certain genes
   3.Better adapted individuals are more likely to survive
3. Also more likely to pass on their advantageous allele via breeding so alleles inherited by next generation
4. Over many generations, the advantageous allele frequency increases
5. Selection pressure determines the spread of an allele within the gene pool

Question 4

What are the different types of selection?

Answer 4

• Stabilising selection
• Directional selection

Question 5

What is stabilising selection?

Answer 5

• Occurs in populations where environment is stable
• Selective pressures at both ends of distribution
• Favours the average
• Eliminates extremes
• Reduces variability
• Reduces opportunity for evolutionary change

Question 6

What is an example of stabilising selection?

Answer 6

• Human birth mass -> babies who are very heavy or light show higher morality rates. Over time selection operates to reduce extremely heavy or light baby weights

Question 7

What is directional selection?

Answer 7

• Mean population represents optimum for existing conditions
• Environmental change may produce new selection pressure that favours the extreme
• When conditions change, the optimum necessary for survival also changes. Some organisms will possess new optimum
• Over time, selection means these will predominate and the mean will shift

Question 8

What is an example of directional selection?

Answer 8

• Bacteria’s ability to resist antibiotics

Question 9

Lactose is the main sugar in milk and is hydrolysed by the enzyme lactase. Lactase is box essential to newborn mammals as milk is their only source of food. Most mammals stop producing lactase when they start feeding on other food sources. Humans are an exception to this because some continue to produce lactase as adults. The ability to continue producing lactase is known as lactase persistence (LP) and is controlled by a dominant allele. A number of hypotheses based on different selection pressures have been put forward to explain LP in humans.

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 farming cattle as a source of milk could have led to an increase in LP. (4)

Answer 9

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

Question 10

Penicillin has been the antibiotic of choice for the treatment of bacterial meningitis. Since the year 2000, strains of Neisseria meningitidis that are resistant to penicillin, sulphonamides and rifampin have been discovered in the UK.
Describe how a population of Neisseria meningitidis (Nm) can become resistant to these antibiotics. (4)

Answer 10

1. Mutation
2. Results in Nm cell with allele for resistance to one antibiotic / to named antibiotic
3. (This) cell survives and passes the allele for resistance to offspring;
4. Process repeated with different genes conferring resistance to each of the other (two) antibiotics