1[1 mark]
Which is a possible disadvantage of selective breeding?
- It increases genetic variation.
- It reduces genetic variation.
- It only takes one generation.
- It involves inserting genes from other species.
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Answer: B B (1)
2[4 marks]
Describe how a farmer could use selective breeding to produce cattle that give more milk.
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- select a bull and cows that produce a lot of milk / with high milk yield (1)
- breed them together (1)
- select offspring that produce the most milk and breed them (1)
- repeat over many generations (1)
3[3 marks]
In a plant, resistance to a disease is controlled by a dominant allele R. Susceptibility is controlled by the recessive allele r. Two plants with the genotype Rr are crossed. Use a genetic diagram to find the probability that an offspring is susceptible.
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- gametes R and r from each parent (1)
- offspring RR, Rr, Rr, rr (1)
- probability of rr = 1/4 or 25% (1)
4
Triple only
[3 marks]Describe how tissue culture can be used to produce new plants.
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- take small pieces of tissue / cells from the parent plant (1)
- use aseptic technique / sterile conditions to prevent contamination (1)
- grow on a nutrient medium (agar) with nutrients and growth hormones (1)
- cells divide to form new plants that are identical to the parent (1)
- Max 3
5
Triple only
[2 marks]Give two advantages of using tissue culture in plant breeding programmes.
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- many identical plants produced quickly (1)
- from a small amount of tissue (1)
- desirable characteristics are kept / plants are genetically identical (1)
- can be done all year / in a small space (1)
- rare / endangered plants can be reproduced (1)
- Max 2
6
Triple only
[2 marks]Explain how tissue culture is useful in medical research.
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- large numbers of identical cells can be grown (1)
- so new drugs can be tested on them / disease can be studied, with reliable results (1)