Modern geneticsEdexcel A-Level Biology B: Topic test

20 questions, 54 marks

Edexcel A-Level Biology B

Modern genetics topic test

Total 54 marks

Name

Class

Date

1
Archaeologists recover a very small amount of DNA from a 3000-year-old mummy. They use the polymerase chain reaction (PCR) to make many copies of one region of the DNA so that its base sequence can be read. The reaction mixture contains primers, nucleotides and Taq polymerase.
(a)
What is the purpose of heating the reaction mixture to about 95 °C at the start of each PCR cycle?
[1 mark]
ATo break the hydrogen bonds between the two DNA strands
BTo make the primers join to the DNA
CTo allow Taq polymerase to work at its optimum temperature
DTo sterilise the reaction mixture
(b)
Starting from one molecule of the target DNA, how many copies of the target are present after 5 complete cycles of PCR?
[1 mark]
A10
B25
C32
D64
(c)
Taq polymerase is obtained from a bacterium that lives in hot springs. Explain why it is suitable for use in PCR.
[2 marks]
Total for question 1: 4 marks
2
Honeybee larvae have identical genomes, but they develop into either sterile workers or fertile queens. Larvae that are fed royal jelly develop into queens. In the cells of queen larvae, the DNA of many genes has fewer methyl groups attached than in worker larvae.
(a)
Which statement describes DNA methylation?
[1 mark]
APhosphate groups are added to bases, which increases transcription.
BMethyl groups are added to DNA, which usually reduces transcription of the gene.
CIntrons are removed from pre-mRNA.
DThe sequence of bases in a gene is altered.
(b)
Which statement best explains why larvae with identical genomes develop into workers or queens?
[1 mark]
AWorkers and queens have different DNA base sequences.
BWorkers have lost some genes through mutation.
CQueens have extra chromosomes.
DDifferent genes are expressed because of epigenetic modification.
(c)
Explain how a high level of methylation of the promoter of a gene in worker larvae could reduce the amount of its protein.
[2 marks]
Total for question 2: 4 marks
3
Researchers want to make maize resistant to an insect pest by inserting a bacterial gene that codes for an insecticidal protein. The gene is delivered into maize cells using a gene gun, together with an antibiotic resistance marker gene.
(a)
Describe how a gene gun can be used to put the bacterial gene into maize cells.
[3 marks]
(b)
Explain how the antibiotic resistance marker gene allows the researchers to identify the maize cells that have taken up the new genes.
[4 marks]
Total for question 3: 7 marks
4
A patient has a blood-clotting disorder. Doctors suspect a fault in the gene for clotting protein P. Sequencing of the coding region of the gene in the patient's DNA shows no mutation, but the patient's liver cells make very little mRNA from the gene. In the patient's liver cells the histones around the gene carry many chemical groups that make the DNA wind tightly round them.
(a)
Describe how PCR and gene sequencing can be used to find the base sequence of the gene for protein P in the patient's DNA and to predict the structure of the protein.
[6 marks]
(b)
Explain how histone modification could lower the amount of protein P in this patient even though the base sequence of the gene is normal.
[6 marks]
Total for question 4: 12 marks
5
Stem cells are found in the bone marrow of an adult and in the very early embryo. A patient with leukaemia receives a transplant of bone marrow stem cells from a donor, and the cells divide and form all of the types of blood cell.
(a)
What does it mean to say that a stem cell is multipotent?
[1 mark]
AIt can form every cell type, including the placenta.
BIt can form any type of cell in the body, but not the placenta.
CIt can form a limited range of related cell types.
DIt can no longer divide.
(b)
Which type of cell in the very early embryo can form every cell type, including the placenta?
[1 mark]
ATotipotent cell
BPluripotent cell
CMultipotent cell
DFully differentiated cell
(c)
Explain why the donor's bone marrow stem cells can form all the types of blood cell but cannot form heart muscle cells.
[2 marks]
Total for question 5: 4 marks
6
Customs officers seize a shipment of ivory. To find out whether two tusks came from the same elephant, scientists extract DNA from each tusk, amplify it by PCR and produce DNA profiles using gel electrophoresis.
(a)
Which of the following describes the genome of an elephant?
[1 mark]
AOnly the genes that are expressed in a particular tissue
BThe proteins made by the elephant's cells
CThe mRNA molecules present in a cell
DAll the DNA in the cells of the elephant, including genes and non-coding sequences
(b)
Which statement about the gel electrophoresis of the PCR products is correct?
[1 mark]
ALonger fragments travel further because they carry more charge.
BShorter fragments travel further because they are hindered less by the gel.
CDNA fragments travel towards the negative electrode.
DThe fragments are separated according to their base sequence, not their length.
(c)
Explain how DNA profiling can show that two tusks came from the same elephant.
[2 marks]
Total for question 6: 4 marks
7
Golden rice has been genetically modified so that the grain makes beta-carotene, which the body converts to vitamin A. A gene from maize and a gene from a soil bacterium were cut out with restriction endonucleases, joined into a plasmid and transferred into rice cells. Vitamin A deficiency causes blindness in children, but some environmental groups oppose growing the rice.
(a)
Describe the roles of restriction endonuclease and DNA ligase in producing the recombinant plasmid.
[3 marks]
(b)
Explain why the widespread use of genetically modified crops such as golden rice has led to public debate. Give two advantages and two concerns.
[4 marks]
Total for question 7: 7 marks
8
A human embryo at day 5 is a blastocyst of about 100 cells. Cells of the inner cell mass can form any cell type of the body, whereas cells of the outer layer form the placenta. A fertility clinic has spare blastocysts, and a research team wants to use them to derive stem cells for research into heart disease.
(a)
Explain how epigenetic modification leads from totipotent cells in the early embryo to differentiated body cells such as heart muscle cells.
[6 marks]
(b)
Evaluate the use of stem cells from spare blastocysts compared with induced pluripotent stem (iPS) cells made from a patient's own skin cells for research into heart disease.
[6 marks]
Total for question 8: 12 marks

End of questions

Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).