4: GENETICS - MUTATIONS

Question 1

What is a gene mutation?

Answer 1

a mutation that involves a change in the DNA base sequence of chromosomes

Question 2

What are 2 types of gene mutations that can occur?

Answer 2

• deletion
• substitution

Question 3

What effect does deletion of a base have on the sequence of amino acids and the polypeptide formed?

Answer 3

• base is deleted so no. of bases changes causing a shift in the base triplets after the point where the base was deleted
• this means there is a change in the sequence of amino acids
• H bonds, ionic bonds and disulfide bridges
• therefore the tertiary structure of the protein is altered
• this means that the protein produced will be non-functional

Question 4

What are the 2 possible effects that the substitution of a base could have on the sequence of amino acids and the polypeptide formed?

Answer 4

• could result in a different sequence of amino acids, which would produce a non-functional protein
• however the substitution could have no effect on the sequence of amino acids as the genetic code is degenerate meaning more than 1 codon can code for a specific amino acid

Question 5

What causes DNA mutations to occur?

Answer 5

• nothing
• mutations occur spontaneously

Question 6

What do mutagenic agents do?

Answer 6

• increase rate of gene mutation
• increase probability of mutation occurring

Question 7

What are examples of mutagenic agents?

Answer 7

• UV radiation
• ionising radiation (eg: X rays, gamma rays)
• chemicals (eg: benzene, bromine, nitrosamines, arsenic)
• viruses (eg: HPV)

Question 8

What are chromosome mutations caused by?

Answer 8

errors during meiosis

Question 9

What do chromosome mutations lead to and why?

Answer 9

• lead to inherited conditions
• this is because the errors are present in the gametes (hereditary cells)

Question 10

What is chromosome non-disjunction?

Answer 10

• failure of the chromosomes to separate properly in meiosis
• so new cells will have an extra copy of the chromosome/ an extra copy of part of the chromosome