Selective breeding, genetic engineering and cloning – GCSE Biology exam questions with mark scheme

1Grade 4–55 marks

Farmers want wheat plants that produce a high yield of grain.

(a) Describe how a farmer could use selective breeding to produce wheat with a high yield. [3]

(b) Give one problem that can result from selective breeding. [1]

(c) Scientists can also produce new varieties of crops by genetic engineering. Give one benefit of genetically modified crops. [1]

(a) choose/select parent plants with (the) high(est) yield
allow plants with the most / largest grains(1)
(a) breed them together / cross-pollinate them(1)
(a) select the offspring with the highest yield and breed them / repeat the process over many generations
allow either idea for this mark(1)
(b) any one from: reduced variation / smaller gene pool (inbreeding); (so) more prone to / all may be killed by a (new) disease; increased chance of inherited defects(1)
(c) any one from: resistant to insect attack / pests; resistant to herbicides; bigger / better fruits or higher yield; produce more nutrients
allow other valid benefits, e.g. resistant to disease / drought tolerant
ignore 'cheaper' / 'better' alone(1)
Answer: (a) Select high-yield parents, breed them, select the best offspring and repeat over many generations (b) e.g. reduced variation, so crops are vulnerable to a new disease (c) e.g. resistance to insect pests.
Examiner tip: The 'repeat over many generations' step is often missed – one cross is not selective breeding.

2Grade 1–3Foundation4 marks

A dog breeder wants to produce puppies that have a gentle nature so they can be used as assistance dogs.

(a) The breeder uses selective breeding. The steps are shown below, but they are in the wrong order.

A Choose the most gentle puppies from the litter and breed them with each other.
B Choose a male dog and a female dog that both have a gentle nature.
C Repeat this over many generations until all the puppies have a gentle nature.
D Breed the two dogs together to produce a litter of puppies.

Write the letters in the correct order. The first one has been done for you. [2]

B → ____ → ____ → ____

(b) Selective breeding is also used by plant growers.

Give one characteristic that plant growers might select for in flowers. [1]

Which statement explains why it is called artificial selection? Tick (✓) one box. [1]

☐ Humans choose which organisms reproduce.
☐ The organisms are made in a laboratory.
☐ Genes from another species are added.
☐ The environment decides which organisms survive.

(a) one or two of D, A, C in the correct position (D second, A third, C fourth)(1)
(a) all correct: B → D → A → C
an answer of B D A C scores 2 marks(1)
(b) any one from: large flowers / unusual flowers / particular colour of flower / strong scent / long-lasting flowers / disease resistance
ignore 'pretty' / 'nice'(1)
(c) Humans choose which organisms reproduce
do not award if more than one box is ticked(1)
Answer: (a) B → D → A → C (b) e.g. large or unusual flowers (c) Humans choose which organisms reproduce
Examiner tip: Selective breeding is always repeated over many generations – an answer that stops after one litter does not describe the process.

3Grade 4–56 marks

A farmer used selective breeding to increase the milk yield of a herd of dairy cows.

The graph shows the mean milk yield of the herd over 10 generations.

(a) Describe the trend shown in the graph. [2]

(b) Calculate the percentage increase in mean milk yield between generation 0 and generation 10.

Give your answer to 2 significant figures. [2]

Explain why this inbreeding could cause problems for the herd. [2]

(a) milk yield increases (as the number of generations increases)(1)
(a) the increase slows down / levels off (after about generation 6)
allow use of data, e.g. increases by 800 litres from generation 0 to 2 but only 100 litres from 8 to 10(1)
(b) (6600 − 4200) ÷ 4200 (× 100)
allow 2400 ÷ 4200 for this mark(1)
(b) 57 (%)
correct answer with no working scores 2 marks
57.1 / 57.14 (not to 2 s.f.) scores 1 mark only(1)
(c) reduces the variation / number of different alleles in the herd
allow cows are genetically very similar(1)
(c) so harmful (recessive) alleles are more likely to be inherited together causing inherited defects / so the cows are more prone to disease / all could be killed by the same disease(1)
Answer: (a) Yield increases, but the increase slows / levels off after about generation 6. (b) 57% (c) Inbreeding reduces variation, so inherited defects and disease are more likely.
Examiner tip: When describing a trend, say what happens to the rate of increase, not just that it 'goes up' – the levelling off is the second mark.

4Grade 4–55 marks

People with Type 1 diabetes need to inject insulin.

In the past, insulin was extracted from the pancreases of pigs. Now, most insulin is made by bacteria that have been genetically engineered to contain the human insulin gene.

(a) What is meant by genetic engineering? [1]

(b) Give two advantages of making insulin using genetically engineered bacteria rather than extracting it from pigs. [2]

(i) Name this type of treatment. [1]

(ii) Suggest why this treatment could cure the disorder rather than just relieve the symptoms. [1]

(a) changing the genome of an organism by introducing a gene from another organism
allow transferring a gene from one organism / species to another
ignore 'changing genes' unqualified(1)
(b) any two from:
• the insulin is human insulin / identical to human insulin, so less likely to cause an (allergic / immune) reaction
• bacteria reproduce quickly so large amounts / a continuous supply can be made
• no animals need to be killed / no ethical or religious objections (e.g. to using pigs)
ignore cheaper / easier unqualified(1)
(b) second advantage from the list(1)
(c)(i) gene therapy
do not accept 'genetic engineering' (given in the stem)(1)
(c)(ii) a working / functional copy of the faulty gene (allele) is added to the person's cells, so the cause of the disorder is corrected
allow the faulty gene is replaced(1)
Answer: (a) Adding a gene from one organism into the genome of another. (b) e.g. it is human insulin so fewer reactions; bacteria reproduce quickly so large amounts made. (c)(i) Gene therapy (ii) It adds a working copy of the faulty gene, so treats the cause.
Examiner tip: 'Cheaper' or 'easier' on its own rarely scores – link each advantage to a reason, e.g. bacteria reproduce quickly so large amounts are made.

5Grade 6–7Higher5 marks

Scientists produced soya bean plants that are resistant to a herbicide (weedkiller). They used a gene from a soil bacterium.

The diagram shows the first stages of the process.

(a) Name the type of ring of DNA labelled X. [1]

(b) What is used to cut the herbicide-resistance gene out of the bacterial DNA in Step 1? [1]

(c) Describe how ring X is then used to produce soya bean plants in which every cell contains the herbicide-resistance gene. [3]

(a) plasmid
do not accept chromosome / nucleus
ignore vector on its own(1)
(b) enzymes
allow restriction enzymes
ignore scissors(1)
(c) X / the plasmid acts as a vector / carries the gene into the soya bean cells(1)
(c) (the gene is inserted into) plant cells at an early stage of development / embryo / a few cells (e.g. fertilised egg or tissue)(1)
(c) so the gene is copied (by mitosis) into all cells as the plant grows / the plant develops with the desired characteristic(1)
Answer: (a) Plasmid (b) Enzymes (c) The plasmid is a vector that carries the gene into soya bean cells at an early stage of development, so as the plant grows by mitosis every cell gets the gene.
Examiner tip: Higher-tier students often lose a mark in (c) by not saying the gene goes in at an early stage of development – that is why every cell ends up with it.

6Grade 6–76 marks

Cotton plants are often damaged by caterpillars. Some farmers grow genetically modified (GM) cotton that contains a gene from a bacterium. The gene makes the cotton produce a toxin that kills caterpillars.

The table shows information collected from farms in one region.

	Non-GM cotton	GM cotton
Mean yield in kg per hectare	1500	1900
Number of insecticide sprays per season	12	4
Cost of seed in £ per hectare	40	110

Evaluate the use of GM cotton by farmers in this region.

Use information from the table and your own knowledge. [6]

For: yield is higher with GM cotton – 400 kg per hectare / about 27% more(1)
For: fewer insecticide sprays (4 instead of 12) – saves money / time / labour for the farmer(1)
For: less insecticide in the environment – fewer harmless / useful insects (e.g. bees, predators of pests) killed; less risk to the farmer's health(1)
For: more cotton produced from the same land, so the farmer earns more / less land needs to be cleared(1)
Against: GM seed costs £70 more per hectare / almost three times as much – poorer farmers may not afford it(1)
Against: concern about effects on wild populations – the gene could spread to wild plants (e.g. by pollen) / toxin may kill non-pest insects that feed on the plant / effect on food chains(1)
Against: caterpillars could become resistant to the toxin (by natural selection), so the benefit would not last(1)
Against: concerns about human health / effects not fully known (e.g. cottonseed oil used in food)(1)
Against: data are from one region / only means given / don't know if the extra yield pays for the extra seed cost(1)
Judgement – e.g. GM cotton is worthwhile because the extra yield and fewer sprays outweigh the higher seed cost, but its effect on wild insects should be monitored(1)

Level	Marks	What it looks like
Level 3	5–6	A balanced evaluation that weighs advantages against disadvantages, uses data from the table with comparisons, includes relevant own knowledge (e.g. effects on wild populations or health) and reaches a conclusion supported by the points made.
Level 2	3–4	Advantages and disadvantages are both given, with some use of the data; there may be a conclusion, but it is not fully justified.
Level 1	1–2	Simple statements of relevant points, which may be one-sided or just copy data from the table without comparison.
No relevant content	0	Nothing worthy of credit.

Answer: Balanced evaluation using the data (higher yield, fewer sprays vs higher seed cost) and own knowledge (wild populations, resistance, health concerns), ending with a justified conclusion.
Examiner tip: Quote numbers from the table and compare them (e.g. '400 kg per hectare more'), then finish with a justified conclusion – without both, an answer cannot reach Level 3.

7Grade 1–3FoundationTriple only4 marks

A garden centre sells a rose plant that has unusual striped flowers.

(a) The gardeners produce new rose plants by taking cuttings.

Give two reasons why they use cuttings rather than growing new plants from seeds. [2]

(b) Scientists use a different method to clone a rare orchid. They take small groups of cells from the orchid and grow them on a jelly containing nutrients and plant hormones.

Name this method of cloning. [1]

Give one disadvantage of this. [1]

(a) any two from:
• new plants are genetically identical to the parent / are clones, so will all have the striped flowers / the desired characteristic
allow plants grown from seed would show variation / might not have striped flowers
• quick(er) (than growing from seed)
• cheap / easy / no special equipment needed
'genetically identical' and 'keeps the striped flowers' together count as one reason(1)
(a) second reason from the list(1)
(b) tissue culture
allow micropropagation(1)
(c) no (genetic) variation, so if one plant gets a disease they could all be killed / all are affected by the same disease or change in conditions
allow all have the same weaknesses(1)
Answer: (a) e.g. plants are genetically identical so all have striped flowers; quick and cheap. (b) Tissue culture (c) No variation, so one disease could wipe out all the plants.
Examiner tip: 'They are the same' is too vague – say the new plants are genetically identical to the parent, so they keep the desired characteristic.

8Grade 6–7Triple only6 marks

A farmer has a prize-winning bull and a prize-winning cow. A vet uses embryo transplants to produce many calves from them.

(a) Describe how embryo transplants are carried out. [2]

(b) The vet produces 4 embryos. Each embryo is split into 6 parts and every part is implanted into a different host cow.

On average, 75% of implanted embryos develop into a calf.

Calculate the number of calves the farmer should expect. [2]

(c) All the calves that come from the same embryo are genetically identical to each other. They are not genetically identical to the prize-winning cow.

Explain why. [2]

(a) (an embryo is produced by fertilisation, then) cells are split apart / the embryo is split (before the cells become specialised)(1)
(a) the identical embryos / cells are transplanted into host (surrogate) mothers(1)
(b) 4 × 6 = 24 (embryos implanted)
allow 6 × 0.75 = 4.5 (calves per embryo)(1)
(b) 24 × 0.75 = 18 (calves)
correct answer with no working scores 2 marks(1)
(c) the calves from one embryo came from the same fertilised egg / have the same genetic information because cells were split from one embryo (cells formed by mitosis)(1)
(c) the embryo was formed by sexual reproduction / fertilisation, so it has a mixture of genes / alleles from the bull and the cow
allow half the genetic information comes from the father(1)
Answer: (a) The embryo is split into separate cells before they specialise and these are transplanted into host mothers. (b) 18 calves (c) All come from one fertilised egg so they share the same DNA, but that egg came from sexual reproduction so has genes from both the bull and the cow.
Examiner tip: In (c) students explain why the calves match each other but forget the second half – the embryo itself came from fertilisation, so it is a mix of both parents.

9Grade 6–74 marks

Plant breeders want to produce tomato plants that are resistant to a fungal disease.

A wild species of tomato is resistant to the disease, but its fruit is small and sour. The wild species can still breed with cultivated tomatoes.

The breeders could use selective breeding or genetic engineering.

Compare these two methods of producing disease-resistant tomato plants. [4]

Similarity: both produce plants with a desired characteristic / both change the genes (alleles) of the crop / both involve humans choosing the characteristic
(max 1 mark for similarities)(1)
selective breeding takes many generations / a long time, whereas genetic engineering can produce the resistant plant in one generation / more quickly(1)
selective breeding transfers many genes at once so unwanted characteristics (e.g. small, sour fruit) may also be inherited, whereas genetic engineering transfers only the resistance gene
allow genetic engineering is more precise / targeted(1)
genetic engineering can use a gene from any species (including bacteria / other organisms), whereas selective breeding only works with organisms that can breed together / the same (or closely related) species
allow genetic engineering is more expensive / needs specialist laboratory equipment; GM crops face more public concern (about wild populations / health); selective breeding can reduce variation (inbreeding)(1)
Answer: Both give plants with a desired characteristic, but selective breeding takes many generations and brings in unwanted genes (small, sour fruit) and only works with species that interbreed; genetic engineering transfers just the resistance gene, from any species, in one generation.
Examiner tip: 'Compare' needs both methods in the same sentence – use 'whereas'. Describing selective breeding and then genetic engineering separately often scores only 1–2 marks.

10Grade 6–7Triple only6 marks

Scientists used adult cell cloning to produce a lamb. The diagram shows the method.

(a) The lamb was born with a black face.

Explain why the lamb has a black face, even though it developed inside Sheep C. [2]

(b) Give the reason the scientists used an electric shock. [1]

(c) In one series of experiments, the scientists fused 340 egg cells with adult nuclei. 41 of these grew into embryos, but only 2 lambs were born alive.

Calculate the percentage of fused egg cells that produced a live lamb. [2]

(d) Using your answer to (c), give one ethical objection to adult cell cloning of animals. [1]

(a) the nucleus / genetic material / DNA came from Sheep A(1)
(a) any one from:
• Sheep C only provides the uterus / does not provide any genes / DNA to the lamb
• the egg from Sheep B had its nucleus removed, so it has none of B's genes / DNA
• the lamb is a clone of / genetically identical to Sheep A, and genes control face colour(1)
(b) to stimulate the egg cell to divide (by mitosis) / to make it start developing into an embryo
allow to make the nucleus fuse with the egg cell
ignore 'to start it' unqualified(1)
(c) 2 ÷ 340 × 100(1)
(c) 0.59 (%)
allow 0.588 / 0.6(1)
(d) very low success rate (only about 0.6% / 2 out of 340), so most embryos die / are wasted / many surrogate pregnancies fail, which could cause suffering
allow many animals / eggs are used to produce very few lambs
ignore 'playing God' / 'unnatural' unless linked to the low success rate(1)
Answer: (a) The nucleus (DNA) came from Sheep A; the egg from B had its nucleus removed and C only provides the uterus. (b) To make the egg cell start dividing to form an embryo. (c) 0.59% (d) e.g. very low success rate – many embryos die / animals suffer.
Examiner tip: In (a) 'it came from A' is not enough – say that the nucleus or genetic material came from Sheep A, because genes determine features like face colour.

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