Inheritance T2

Question 1

Describe the difference between somatic gene therapy and germ line gene therapy.
(2)

Answer 1

• Somatic involved body cells and and germ line involves gametes.
• Somatic can’t be inherited, germ line can.
• Somatic is legal, germ line is illegal.
• Somatic is only temporary, germ line could cure.

Question 2

Suggest how somatic gene therapy could enable cells lining the lungs to function normally
in people with cystic fibrosis.
(4)

Answer 2

• Vector i.e. plasmid or virus.
• Inserting functional gene that codes for the CFTR protein.
• Using nebuliser to get into lungs.
• CFTR protein made via transcription/translation.
• Allows chloride ions to leave cell.
• So water drawn out of cell via osmosis.
• So mucus is less sticky.

Question 3

Rhythmical tapping of the chest wall during physiotherapy can relieve the symptoms of
cystic fibrosis in the lungs.
Suggest an explanation for this.
(2)

Answer 3

• Loosens mucus.
• So mucus expelled from lungs more easily.
• So clearer airways/better breathing.

Question 4

Cystic fibrosis is an inherited condition.
Explain why people with cystic fibrosis can have breathing difficulties.
(4)

Answer 4

• Produces thicker/stickier mucus.
• Blocking trachea/ bronchi/ airway.
• Cilia unable to move mucus out of lungs.
• Reduced flow of oxygen to alveoli.
• Reduced concentration gradient of oxygen/carbon dioxide in alveoli.
• Loss of surface area.
• Reduced gas exchange.
• Trapped bacteria may result in more respiratory infections.

Question 5

Explain the meaning of the term recessive allele.

3

Answer 5

• Both alleles need to be present for recessive phenotype to be expressed.
• Different form of a gene.
• Same locus.
• Dif. base sequence.

Question 6

Mutations to DNA can affect the structure of proteins produced in the cell.
Removing one base from a DNA sequence will affect the primary structure of a protein.
Changing one base for another may not affect the primary structure of a protein.
Explain why these two types of mutation have different effects on protein structure.
(4)

Answer 6

• Deletion could affect every codon on the mRNA. Substitution will only affect one codon. Frame shift.
• Deletion more likely to affect position of start and stop codon.
• Deletion results in a different sequence of amino acids. Substitution may not affect sequence.
• Substitution may code for same amino acid due to degenerate nature of genetic code.

Question 7

Leptin is a protein hormone with a role in the control of appetite in humans.
Several mutations of the leptin gene have been identified. All these mutations are frameshift
mutations that result in shortened primary structures.
A frameshift mutation involves the insertion or removal of one or two nucleotides from a gene.
Describe how a frameshift mutation could result in the production of leptin with a variety of
shorter primary structures.
(2)

Answer 7

• Adding or removing nucleotides changes the triplet code.
• Introducing a new start/stop codon.
• Coding for a shorter sequence of amino acids.