What is breeding?
Breeding means people choose which plants or animals will be the parents of the next generation. We choose parents that have a trait we like, such as more grain, more milk, or less disease. Over many generations that trait becomes common.
Breeding works because of heredity: children get genes from parents. If good genes are passed on again and again, the whole group improves.
Domestication
Domestication means taking a wild species and slowly changing it so it lives with people and gives us food, work or fibre. Wild wheat drops its seeds by itself, which is bad for a farmer. Plants that kept their seeds on the stalk were easier to harvest, so farmers saved those seeds. After many years the crop kept its seeds on the stalk.
Animals changed too. Wild cattle were fierce and gave little milk. People kept the calmer, better milkers, and today's cows are very different from their wild ancestors.
Domestication began about 10,000 years ago, when people started farming.
Artificial selection and other methods
In natural selection nature decides who survives. In artificial selection the breeder decides who gets to have babies.
- Selection: pick the best individuals and use only them as parents.
- Hybridisation: cross two different varieties to mix their good traits. The first-generation hybrid is often stronger than both parents. This is called heterosis or hybrid vigour.
- Inbreeding: mating close relatives keeps a trait fixed but can weaken the group over time.
- Mutation breeding: radiation or chemicals change genes at random, and the breeder keeps any useful change.
Vavilov and the centres of origin
The Russian botanist Nikolai Vavilov collected crop seeds from many parts of the world in the early 1900s. He noticed that each crop shows the greatest number of varieties, and has its wild relatives, in one region. He called such a region the crop's centre of origin (for example, wheat and barley in the Near East, rice in South and South-East Asia, maize in Central America, potato in the Andes).
These regions are a treasure store of genes. Breeders go back to wild relatives there to find resistance to disease or drought. Vavilov also noted that related species show similar patterns of variation, called the law of homologous series.
Try it
In the 3D, pick the tallest three plants five times and write down the average height after each generation. Then press Reset and pick the shortest three. Does the average go down? At home, save seeds from the biggest tomato or chilli for a season and compare the next crop.
Key formulas and definitions
- Domestication = wild species changed by people over many generations
- Artificial selection: breeder chooses the parents
- Hybridisation: cross of two varieties; F1 may show heterosis
- Centre of origin: region with most varieties and wild relatives of a crop (Vavilov)
Worked examples
1. A farmer has 20 plants and keeps 4 for seeds. What percent were chosen?
4 out of 20 is 4/20 = 0.2, which is 20 percent.
2. The average height of a crop is 70 cm. The chosen parents average 90 cm. What is the selection difference?
90 โ 70 = 20 cm. The bigger this gap, the faster the crop can change in the next generation.
3. A wheat variety gives high yield but gets rust disease. Another resists rust but gives low yield. How can a breeder get a good wheat?
Cross them (hybridisation). Grow the offspring and keep plants that have both high yield and rust resistance. Repeat for a few generations to make the trait stable.
4. Why do breeders visit the centre of origin of a crop?
Because it holds the most variety and the wild relatives. These have genes for disease and drought resistance that farm varieties may have lost.
Common mistakes
- Thinking breeding is the same as genetic engineering. Breeding mixes whole organisms; genetic engineering moves single genes.
- Saying plants "decide" to change. Change happens because the farmer chooses certain parents each time.
- Believing one generation of selection is enough. Real improvement takes many generations.
- Mixing up the centre of origin with the place where a crop grows most today. It is where the crop has most variety.