AQA GCSE Combined Science (8464), Higher tier · Biology › Inheritance, variation and evolution › Variation and evolution
Practise Selective breeding. 11 exam-style questions plus unlimited generated ones on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
Selective breeding (artificial selection) is humans breeding plants and animals for particular genetic characteristics. You need the steps, examples and the problem of inbreeding. Questions include 'describe how a farmer could breed...' and explaining or evaluating its impact.
Grade by grade
What you need to be able to do, from the first marks up to the top grade.
3
Define selective breedingHumans breeding plants and animals for particular genetic characteristics.
4
Give examples of chosen characteristicsDisease resistance in crops, more meat or milk, gentle dogs, large or unusual flowers.
5
Describe the steps of selective breedingChoose parents with the characteristic, breed them, select the best offspring, and repeat over many generations.
6
Explain the problems caused by inbreedingBreeds become prone to disease or inherited defects because variation is reduced.
7
Compare selective breeding with natural selectionIn selective breeding humans choose which individuals breed; in natural selection the environment decides which survive to breed.
7
Evaluate the impact of selective breedingWeigh benefits such as more food against inbreeding and reduced variation.
Notes
What selective breeding is
Selective breeding (artificial selection) is the process by which humans breed plants and animals for particular genetic characteristics.
Humans have done this for thousands of years, since they first bred food crops from wild plants and domesticated animals.
The steps
Choose parents with the desired characteristic from a mixed population.
Breed them together.
From the offspring, choose those with the desired characteristic and breed them together.
Repeat over many generations until all the offspring show the desired characteristic.
Characteristics that are chosen
Characteristics can be chosen for usefulness or for appearance.
Disease resistance in food crops.
Animals that produce more meat or milk.
Domestic dogs with a gentle nature.
Large or unusual flowers.
Problems
Selective breeding can lead to inbreeding (breeding closely related individuals), so some breeds are particularly prone to disease or inherited defects.
Inbreeding reduces genetic variation, so offspring are more likely to inherit two copies of a harmful recessive allele. grade 7+
With little variation, a new disease or a change in the environment could affect all the individuals in a breed.
Steps: choose parents with the characteristic → breed → select the best offspring → breed → repeat over many generations
Examples: disease-resistant crops, more meat or milk, gentle dogs, large or unusual flowers
Inbreeding → breeds prone to disease and inherited defects
Natural selection: the environment decides which individuals survive to breed. Selective breeding: humans choose
How to answer each type of question
Describe how to selectively breed for a characteristic
3 to 4 marks5
Choose parents that show the characteristic.
Breed them together.
Select the offspring with the characteristic and breed them.
Repeat over many generations.
Example. A farmer wants to produce a herd of cows that produce a large volume of milk. Describe how the farmer could use selective breeding to do this. [4 marks]
Show the model answer
Choose the cows that produce the most milk, and a bull from a line of high-yielding cows (1). Breed these cattle together (1). Select the offspring that produce the most milk and breed them together (1). Repeat this over many generations (1).
Explain the problems of selective breeding
2 to 3 marks6
Say that it can lead to inbreeding (closely related animals are bred together).
This reduces variation.
So there is a greater risk of inherited defects and disease, and a new disease could affect them all.
Example. Some breeds of dog have been selectively bred from a small number of closely related animals. Explain why dogs of these breeds are more likely to have inherited disorders. [3 marks]
Show the model answer
Breeding closely related dogs is inbreeding (1). This reduces genetic variation in the breed (1). So the dogs are more likely to inherit two copies of a harmful recessive allele (1).
Compare selective breeding with natural selection
2 to 3 marks7
Give a similarity: in both, individuals with certain characteristics breed and pass on their alleles over many generations.
Give the key difference: who or what does the choosing.
Add what is selected: characteristics useful to humans, or characteristics that help survival.
Example. Compare selective breeding with natural selection. [3 marks]
Show the model answer
In both, individuals with certain characteristics breed and pass on their alleles over many generations (1). In selective breeding, humans choose which individuals breed, whereas in natural selection the environment determines which individuals survive to breed (1). Selective breeding selects characteristics that are useful to humans, whereas natural selection selects characteristics that help survival in that environment (1).
Shortcuts and memory tricks
Selective breeding recipe: select, breed, select, breed... for many generations.
Inbreeding = breeding within the family: less variation, more inherited defects.
Leaving out 'over many generations'. Selective breeding takes a long time.
Confusing selective breeding with genetic engineering. No genes are moved between organisms in selective breeding.
Saying selective breeding creates new alleles. It only selects from the variation that already exists.
Saying inbreeding directly causes disease. It makes inherited defects more likely because variation is reduced.
Exam technique
In 'describe' questions, give the steps in order, including selecting the offspring and repeating.
Use the organism and characteristic in the question (e.g. 'cows that produce the most milk').
For 'evaluate' questions, give benefits and problems, then a conclusion.
Quick recall
Cover the answers and test yourself. The app has these as flashcards that come back just before you'd forget them.
Give two characteristics that farmers might choose when selectively breeding food crops or farm animals.
E.g. disease resistance in crops; high yield; animals that produce more meat or milk
All of these vegetables still belong to the same species. What does this tell you about them?
They can interbreed to produce fertile offspring
Give the name of the process in which humans choose organisms with desired characteristics and breed them together over many generations.
Selective breeding
Sample questions
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy5 marks
Humans have used selective breeding for thousands of years.
(a) What is selective breeding? Tick (✓) one box.[1]
Changing an organism's genome by adding a gene from another organism
Growing new plants from small groups of cells
Humans choosing parents with desired characteristics and breeding them together
The survival of the organisms best suited to their environment in the wild
(b) Give two characteristics that farmers might choose when selectively breeding food crops or farm animals.[2]
(c) The steps in selective breeding are given below, but they are in the wrong order. A Breed together the offspring that show the desired characteristic. B Choose parents with the desired characteristic from a mixed population. C Repeat over many generations until all the offspring show the characteristic. D Breed the chosen parents together. Write the letters in the correct order.[2]
Show the answer and mark scheme
(a)Answer: Humans choosing parents with desired characteristics and breeding them together
(b)Answer: E.g. disease resistance in crops; high yield; animals that produce more meat or milk
disease resistance (in food crops)
animals that produce more meat
animals that produce more milk
higher yield / bigger fruit or grain
(c)Answer: B, D, A, C
B first and C last
D before A
Question 2Medium6 marks
Cabbage, broccoli, cauliflower, kale and Brussels sprouts have all been produced by selective breeding from the same species of wild plant.
(a) Broccoli has very large flower heads. Describe how farmers produced broccoli from the wild plant.[3]
(b) All of these vegetables still belong to the same species. What does this tell you about them?[1]
(c) Plant breeders also select crops for disease resistance. Give two benefits of growing disease-resistant crops.[2]
Show the answer and mark scheme
(a)Answer: Chose wild plants with the largest flower heads and bred them together; chose the offspring with the largest flower heads and bred them; repeated this for many generations
choose plants with the largest flower heads
breed them together and select offspring with the largest flower heads (to breed)
repeat over many generations
(b)Answer: They can interbreed to produce fertile offspring
they can interbreed to produce fertile offspring
(c)Answer: Higher yields; less need for pesticides / fungicides, which saves money and harms the environment less
higher yield / less crop lost
less need to spray pesticides / fungicides
lower costs for the farmer
more reliable food supply / food security
Question 3Hard7 marks
Many breeds of dog have been produced by selective breeding. To keep the characteristics of a breed, breeders often mate closely related dogs. This is called inbreeding. In one breed, a large number of dogs have an inherited eye disorder caused by a recessive allele.
(a) Explain why inbreeding increases the chance that puppies will have a disorder caused by a recessive allele.[3]
(b) Explain why selective breeding reduces the genetic variation within a breed.[2]
(c) A test has been developed that shows whether a dog carries the allele for the eye disorder. Suggest how breeders could use the test to reduce the number of puppies born with the disorder.[2]
Show the answer and mark scheme
(a)Answer: Related dogs share many of the same alleles, so both parents are more likely to carry the same recessive allele; each puppy is then more likely to inherit two copies and be homozygous recessive
related dogs share many of the same alleles
so both parents are more likely to carry the (same) recessive allele
so puppies are more likely to inherit two copies / be homozygous recessive
(b)Answer: Only a few dogs with the chosen characteristics are bred, so other alleles are lost from the breed
only dogs with certain characteristics are used for breeding / only a few parents are used
so some alleles are lost / fewer different alleles in the breed
(c)Answer: Test dogs before breeding and never mate two carriers together; breed carriers only with dogs that do not carry the allele (or do not breed from carriers)
test dogs before breeding
do not mate two carriers together / only breed carriers with non-carriers / do not breed from carriers