Selective breeding: the basic process
The idea in one sentence
Selective breeding (also called artificial selection) is when humans choose which organisms breed together, so that a desired characteristic becomes more common over many generations.
Nature does not choose the parents — a farmer, breeder or plant scientist does.
The four steps you must be able to write
Whatever the organism, the same sequence earns the marks:
- From a population showing variation, select the individuals with the desired characteristic (e.g. highest wheat yield, most milk).
- Breed these selected individuals together (cross-pollinate the plants; mate the animals).
- From the offspring, again select those that show the desired characteristic best.
- Repeat over many generations until all offspring reliably show the characteristic.
That final phrase — repeated over many generations — is a mark on its own in almost every selective breeding question. Do not leave it out.
Why it works
The desired characteristic is controlled by genes. Parents with the characteristic pass those alleles to their offspring, so each generation contains a higher proportion of individuals carrying them. Selective breeding does not create new genes — it changes how common existing ones are.
Things it is easy to lose marks on
- Offspring are not identical to the parents. Fertilisation is a random process, so which gametes fuse — and therefore which alleles the offspring get — varies. That is exactly why breeders must repeat the selection every generation instead of stopping after one cross.
- Selective breeding is not genetic engineering. No genes are transferred between organisms; you are only choosing parents.
- Variation must already exist in the population. If every plant is the same height, you cannot select for tallness.
Common mistake: writing that breeders "make" or "create" a new characteristic. Say instead that they select organisms that already show it and breed from them.
Examiner tip. Candidates often lose marks because they answer a slightly different question from the one asked. Read every word of the stem: a question about plants wants pollination and seeds, a question about cattle wants mating, and a question that says 'explain' wants reasons, not just the steps.