AQA A level Bio 4.3 Genetic diversity via Mutation

Chemotherapy is the use of a drug to treat cancer. The drug kills dividing cells.
The figure below shows the number of healthy cells and cancer cells in the blood of a patient receiving chemotherapy. The arrows labelled F to I show when the drug was given to the patient.

Describe similarities and differences in the response of healthy cells and cancer cells to the drug between times F and G. (3)

(similarities) :

same/similar pattern (1)

Number of cells stays the same for same length of time (1)

(differences) :

(per unit volume of blood)

Greater/faster decrease in the number of healthy cells

Read the following passage.

The sequence of bases in a molecule of DNA codes for proteins. Different sequences of bases

code for different proteins. The genetic code, however, is degenerate. Although the base

sequence AGT codes for serine, other sequences may also code for this same amino acid.

There are four base sequences which code for the amino acid glycine. These are CCA, CCC,

5       CCG and CCT. There are also four base sequences coding for the amino acid proline. These

are GGA, GGC, GGG and GGT.

Pieces of DNA which have a sequence where the same base is repeated many times are called

“slippery”. When “slippery” DNA is copied during replication, errors may occur in copying.

Individual bases may be copied more than once. This may give rise to differences in the

10     protein which is produced by the piece of DNA containing the errors.

Use information in the passage and your own knowledge to answer the following questions.

Explain how copying bases more than once may give rise to a difference in the protein (lines 9 – 10). (2)

Changes base sequence (1)
Of later triplets (1)

Read the following passage.

The sequence of bases in a molecule of DNA codes for proteins. Different sequences of bases

code for different proteins. The genetic code, however, is degenerate. Although the base

sequence AGT codes for serine, other sequences may also code for this same amino acid.

There are four base sequences which code for the amino acid glycine. These are CCA, CCC,

5       CCG and CCT. There are also four base sequences coding for the amino acid proline. These

are GGA, GGC, GGG and GGT.

Pieces of DNA which have a sequence where the same base is repeated many times are called

“slippery”. When “slippery” DNA is copied during replication, errors may occur in copying.

Individual bases may be copied more than once. This may give rise to differences in the

10     protein which is produced by the piece of DNA containing the errors.

Use information in the passage and your own knowledge to answer the following questions.

Different sequences of bases code for different proteins (lines 1 – 2). Explain how. (2)

Protein made of (chain of) amino acids (1)
each amino acid has its own base/triplet (1)

1