Unit 4 - 3.4.4 Genetic diversity and adaptation

Question 1

All mammals produce a lipase called CEL.

Mammals feed their young on milk. CEL digests the triglycerides in milk. The ability to produce CEL occurred due to a gene mutation.

Describe how natural selection may have led to all mammals in a population producing CEL. (4)

Answer 1

1. Mutation results in (a new) allele;
2. Those with the (new) allele able to digest milk/triglycerides;
3. Individuals with CEL/allele more likely to (survive and) reproduce;
4. Directional selection;
5. Increase in frequency of (this) allele in population;

Question 2

The human disease, malaria, is caused by infection with a single-celled eukaryotic organism.

Plasmodium vivax is one of the species that can cause malaria.

In Africa today, most of the human population are resistant to malaria caused by P. vivax.

Use your knowledge of natural selection to explain why this resistance is so common in Africa. (4)

Answer 2

1. Mutation produced allele;
2. Those with allele/resistance less likely to/do not get malaria/P vivax
   OR
   Those with allele/resistance survive malaria/P vivax;
3. (So more likely to) reproduce and pass on the allele;
4. (Over generations) allele frequency increases;

Question 3

Define ‘gene mutation’ and explain how a gene mutation can have:

• no effect on an individual
• a positive effect on an individual. (4)

Answer 3

For 4 marks at least one mark must be scored in each section of the answer.

(Definition of gene mutation)

1. Change in the base/nucleotide (sequence of chromosomes/DNA);
2. Results in the formation of new allele;

(Has no effect because)

3. Genetic code is degenerate (so amino acid sequence may not change);
   OR
   Mutation is in an intron (so amino acid sequence may not change);
4. Does change amino acid but no effect on tertiary structure;
5. (New allele) is recessive so does not influence phenotype;

(Has positive effect because)

6. Results in change in polypeptide that positively changes the properties (of the protein)
   OR
   Results in change in polypeptide that positively changes a named protein;
7. May result in increased reproductive success
   OR
   May result in increased survival (chances);

Question 4

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, sulfonamides and rifampin have been discovered in the UK.

Describe how a population of Neisseria meningitidis (Nm) can become resistant to these antibiotics. (4)

Answer 4

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

Question 5

HIV attaches to a specific protein receptor on helper T cells. A low percentage of people have a mutation of the CCR5 gene which codes for this protein receptor. This mutation results in a non-functional protein receptor.

Explain how this mutation can result in the production of a non-functional protein receptor. (4)

Answer 5

1. Change in DNA base/nucleotide (sequence);
2. Change in amino acid (sequence)/primary structure;
3. Alters (position of) hydrogen/ionic/disulfide bonds;
4. Change in tertiary structure (of receptor);

Question 6

What is meant by genetic diversity? (1)

Answer 6

Differences in DNA / differences in base sequence of DNA;
(Accept: number of different alleles / size/variation in gene pool)

Question 7

A mutation can lead to the production of a non-functional enzyme. Explain how. (6)

Answer 7

1. Change / mutation in base / nucleotide sequence (of DNA / gene);
2. Change in amino acid sequence / primary structure (of enzyme);
3. Change in hydrogen / ionic / disulfide bonds;
4. Change in the tertiary structure / shape;
5. Change in active site;
6. Substrate not complementary / cannot bind (to enzyme / active site) / no enzyme-substrate complexes form.

Question 8

People with Ellis-van Creveld syndrome have heart defects, are short and have extra fingers and toes. Ellis-van Creveld syndrome is caused by a faulty allele.

This mutation leads to the production of a protein that has one amino acid missing.

Suggest how the production of a protein with one amino acid missing may lead to a genetic disorder such as Ellis-van Creveld syndrome. (2)

Answer 8

1. Change in tertiary structure / active site;
2. (So) faulty / non-functional protein / enzyme;

Question 9

The spotted owl is a bird. Numbers of spotted owls have decreased over the past 50 years. Explain how this decrease may affect genetic diversity. (2)

Answer 9

Reduced (genetic diversity);

As fewer different / varied alleles / genes / reduced gene pool;

Question 10

Some antibiotics bind with specific receptors in the plasma membranes of bacteria. The structure of these receptors is determined genetically. Bacteria can become resistant to an antibiotic because a gene mutation results in an altered receptor.

Explain how resistance to an antibiotic could become widespread in a bacterial population following a gene mutation conferring resistance in just one bacterium. (5)

Answer 10

1. frequent use of antibiotic creates selection pressure / antibiotic kills bacteria;
2. bacteria with mutation / resistance have (selective) advantage over others / described;
3. (survive to) reproduce more than other types pass on advantageous allele / mutated allele in greater numbers;
4. frequency of (advantageous) allele increases in subsequent generations;
5. frequency of resistant types increases in subsequent generations;