6.19 Selective breeding
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Describe how a farmer could use selective breeding to produce cows that give more milk.
Mark scheme
- choose cows / parents with high milk yield (1)
- breed them together (1)
- select offspring with highest milk yield and breed them (1)
- repeat over many generations (1)
Model answer
The farmer chooses the cows that produce the most milk and breeds them with a bull from a high-yield line. From the offspring, the cows with the highest yield are chosen and bred. This is repeated over many generations.
Give two characteristics that plants or animals are selectively bred for.
Mark scheme
Any two from:
- disease resistance (1)
- more meat / milk (1)
- gentle nature (1)
- large / unusual flowers (1)
- higher crop yield (1)
Model answer
Disease resistance in crops, and more milk in cows.
Explain why inbreeding can cause problems.
Mark scheme
- reduced variation / alleles (1)
- more likely to inherit harmful recessive alleles / inherited defects / prone to disease (1)
Model answer
Inbreeding reduces variation and makes it more likely that offspring inherit two copies of a harmful recessive allele, so some breeds are prone to diseases or defects.
Give one difference between selective breeding and natural selection.
Mark scheme
selective breeding: humans choose which individuals breed; natural selection: environment / survival decides
Model answer
In selective breeding humans choose which individuals breed; in natural selection the environment decides which survive to breed.
Suggest why a field of a selectively bred wheat variety could be wiped out by a new fungal disease.
Mark scheme
- little variation (1)
- so no / few plants resistant to the new disease (1)
Model answer
The wheat plants have very little variation, so it is likely that none of them are resistant to the new disease.
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