Selective breeding chooses which individuals breed, generation after generation. Gene insertion moves a chosen gene straight into an organism. The exam usually asks you to name which method is described, compare them, or say what each can and cannot do.
Selective breeding builds on variation and selection, and gene insertion on the stage-by-stage idea in outlining genetic modification.
How do the two methods work?
Selective breeding:
- Decide the feature wanted, such as higher milk yield.
- Choose the parents that show it most clearly.
- Breed them, then pick the offspring that show it most strongly to breed again.
- Repeat for many generations.
It relies on existing variation. No new alleles are added on purpose, so the change is limited to what the species already contains.
Gene insertion: a specific gene is cut from a donor and placed into the recipient’s DNA. The recipient can gain a feature it has never had, sometimes from a different species, and the change happens in the treated organism rather than over generations of breeding.
Comparing them
| Point | Selective breeding | Gene insertion |
|---|---|---|
| Source of the feature | Variation already in the species | A chosen gene, possibly from another species |
| Time | Many generations | The change is made directly in the organism |
| Precision | Whole sets of genes are passed on together | One chosen gene is targeted |
| Needs | Breeding individuals that can mate | Knowledge of the gene and a way to transfer it |
Worked example
The figures are invented. A farmer breeds cattle for milk yield. The mean yield of the herd in four successive generations is 18, 20, 22 and 24 litres per day.
Question: Explain how this was achieved and calculate the mean increase per generation.
Step 1, describe the method. In each generation the cows with the highest milk yield were bred with bulls whose mothers had high yields.
Step 2, link to variation. Some cows already had alleles giving higher yield, so the offspring of chosen parents tended to have higher yield.
Step 3, calculate. From the first to the fourth generation is 3 steps. 24 − 18 = 6 litres. 6 ÷ 3 = 2 litres per day per generation.
Step 4, compare. Inserting a gene for higher yield would act on one organism directly, while this route took four generations.
The mistake to watch for
Mistaken answer: “In selective breeding, scientists add a gene for high yield.”
No gene is added. The farmer uses the alleles already present. Writing “added a gene” turns the description into gene insertion and loses the marks.
The correction is to use the verb choose for selective breeding (“chose the highest yielding cows to breed”) and the verb insert for gene modification.
Check yourself
1. A rice plant is given a gene from a bacterium that protects it from an insect pest. Which method is this?
Show answer
Gene insertion (genetic modification), because a gene from another species was transferred directly.
2. Give two differences between selective breeding and natural selection.
Show answer
In selective breeding people choose which individuals breed, and the feature wanted is decided by people. In natural selection the environment decides who survives and reproduces, so the features that become common suit the environment.
3. A herd’s mean egg mass rises from 52 g to 58 g over three generations. What is the mean rise per generation?
Show answer
58 − 52 = 6 g. 6 ÷ 3 = 2 g per generation.
Where this leads next
The final skill in the module is evaluating a biotechnology claim, which asks you to judge either method. You can try the inheritance model board to see how chosen parents change the pattern of alleles in a fictional population.
Comparison questions reward a clear sentence that puts both methods in the same frame, and that is something a teacher can coach in online one-to-one Biology tuition. The module page lists the other lessons.